The Soft Spot E-mail Series

The following is the to-date series of e-mail updates sent to the pool industry by onBalance. New updates are being added regularly. If you wish to be added to the recipient list for the emails, contact us with your email address. You may also remove your email address by sending us a note to the same address.

(1) Introduction to plaster spotting

You've heard of the controversy about plaster spots. Some call them spot etching, some call them soft spots. Some recognize them as a unique problem, some try to lump them in with general "etching." Here is a picture of a pool with spots. If you could touch it, it would be smooth - so smooth you couldn't locate the light spots from the surrounding paste by touch alone. Have you wondered what really causes this problem? Why is there a difference of opinion about the cause? We hope, through this series of email updates, to help you see what the problem is, and why the difference of opinion exists.

(2) A description of plaster spots

Plaster "spotting" became an industry issue in the 1980's. These spots are generally about the size of a dime, and are usually much whiter than surrounding areas of the plaster (both white and colored plaster). Sometimes the spots become tan or aqua over time by absorbing dissolved iron or copper. Sometimes the phenomenon follows the edge of tile, highlights plaster cracks, or follows a troweled radius, or outlines low spots in the plaster.
One of the main characteristics of plaster spots is that the spots are surrounded by smooth, dense, intact plaster. Look at the picture again. Although aggregate (sand) is visible in the spotted area itself, the surrounding area is smooth cement paste.
Also - even though the spot shows aggregate, the spot is relatively smooth. In these samples, from actual pools, you cannot find the spots by touch alone, with your eyes closed.
What could cause a spot like this in otherwise "good" plaster? Answering this question will be key to any true definition of plaster spotting: Does the answer tell us why the plaster is smooth, and has both "bad" spots and "good" surrounding plaster paste - all right next to each other in the same pool?

(3) A few technical terms defined

To understand spotted plaster, we need to have a common vocabulary.

• According to correct terminology, leaching is the capability if water (any water, regardless of its chemical characteristics) to act as a solvent - i.e., to dissolve things. Water is popularly called "the universal solvent" because it can solubilize stuff just by being water. Of course, some soft "soluble" materials will dissolve in seconds, other materials may require days, weeks, months, years - even centuries or millennia to dissolve in normal water.
• Another, different issue is etching, which means water which can dissolve stuff specifically because of a chemical aggressiveness. In swimming pools, an example of etching is water that has low pH, alkalinity, hardness, etc., which makes it preferentially aggressive to plaster, which is highly alkaline (the opposite of acid).

Can we apply one or the other of these terms to plaster spots? Which one is right?

(4) Are we using the right words?

In the 1980s, this plaster spotting phenomenon became popularly known by the slang term "spot etching."

Using the term "spot" is understandable - just look at the pictures!

However, is the use of the term "etching" appropriate? It implies, as we have discussed, that the water in the pool had acidic or aggressive characteristics that were the direct cause of the spots. But the fact of the matter is that it has never been proven that the spots are actually etched! There is no evidence, no documentation - nothing but the implication of aggressive attack by using the term "etch."

Lately in our industry there has been a specific, pre-planned agenda to solve the spotted plaster controversy by simply renaming the phenomenon! Plasterers who originally coined the term "spot etching" now wish to simply call the spots "etching deterioration"!

They feel that this is justified since (in their thinking) the spots are obviously etched… after all, what have we been calling them for the past few decades? Spot etching, of course!

That is redefinition by fiat - not science.

Also, this tactic does not explain why there could even conceivably be "etched" spots, surrounded by unetched paste! This is a problem. Is "aggressive water" intelligent and selective? Will it preferentially attack only localized, dime-sized spots?

(5) Who loses and who gains by using the right or the wrong terms?

Although it is always best when we as an industry can work together to solve problems and make happy consumers, there is a lot at stake when it comes to who causes a plaster surface problem of this type - since the problem can only be cured by replastering the pool - an expensive proposition.

The swimming pool plastering industry, spearheaded by the National Plasterers Council, adopted an official position in their 2002 Technical Manual, that plaster spots are etching, the direct result of improper water chemistry (in fact, the plasterers claim responsibility for coining the "slang" term "spot etching.") They offered no substantive, scientific proof to back their position about an aggressive water cause.

We, on the other hand, would like to share with you (in the next few update emails in this series) our scientific documentation which proves that plaster spots of this type are not the result of aggressive water chemistry at all - but rather that soft spots in plaster are the direct result of substandard plastering practices. We have, and will continue to provide to the industry the science upon which fact is based - not personal opinion or wishful thinking.

(6) The Role of Calcium Chloride in Plastering Pools

About the same time that plaster spots became an issue in the industry, there was also an increase in the use of calcium chloride, a set accelerant. Increasing the amount of calcium chloride as an additive in pool plaster significantly shortens the amount of time it takes to plaster a pool. The difference can mean, for example, taking only 3 hours to finish a pool instead of maybe 4 hours. That’s good right?

Well, there are downsides to using calcium chloride in cement products. According to the Portland Cement Association (PCA), calcium chloride increases porosity, or decreases density by causing shrinkage to the cement paste. It also alters some of the basic setting reactions, and generates byproduct chemicals in cement that otherwise wouldn’t be there. And it imparts unwanted color (graying) to white cement products. Our studies show that much of the calcium chloride at the plaster surface dissolves into the pool water once the pool is filled, thereby increasing porosity even further.

It has been determined by the cement and concrete industry that no more than two percent calcium chloride dihydrate by weight of cement should ever be used. Although plasterers will often say that pool plaster is very different from concrete, in this instance, the NPC adopted that maximum standard endorsed by the PCA and the American Concrete Institute (ACI).

Remember that 2% standard – we will show that actual pools with soft spots (spot etching) almost always exceed the maximum standard. We will also share with you the findings of professional cement analysis, who conclude that soft spots in pool plaster are directly associated with the excessive paste shrinkage and excess porosity caused by calcium chloride abuse.

(7) Hard Troweling vs. Late Hard Troweling

In order to have a smooth, dense, and durable plaster finish, pool plaster is “hard” troweled – which means that the plaster is troweled with additional force and a higher degree of trowel angle to the plaster surface. Like calcium chloride use vs. abuse, hard troweling can be a good thing if used within reason, and a very bad thing if abused.

Abusive practices relative to hard troweling generally entail too much, too late. If too much hard troweling is done when the plaster is already stiffened to a great degree, then aggregate at the surface is disturbed in its paste bed, without the plaster being capable of “backfilling” or “healing” itself.

According to the American Concrete Institute (ACI), soft or weak plaster can be caused by over troweling or troweling past final set.

Why would a plastering crew need to trowel too hard, too late? Maybe if the plaster was setting (hardening) too fast...?

(8) The Use of Water when Troweling Pool Plaster

In the cement/concrete industry at large, it is very frowned upon to add water while troweling the surface. Why?

• Because water content is the most important factor determining cement durability,
• Because after the surface is hard, only the very top surface of the plaster is resolubilized by the added water, and
• Because at that point the “harder” components (as in less soluble) have already been formed, so adding water only resolublizes the weakest components of the plaster surface.

It is against the rules to add water when troweling. The American Concrete Institute (ACI) says “The use of additional water applied to the surface by dashing with a brush, sprinkling. Or spraying during finishing or edging operations should not be permitted.” (ACI Manual of Concrete Inspection, Detroit: ACI 1981 p. 250) Also, “Especially avoid adding water during hand finishing because this literally washes cement and entrained air out of the surface layer.” (ACI Manual of Concrete Inspection, Detroit: ACI 9th ed. 1999 p. 104)

Unfortunately, this practice has become too common in the swimming pool plastering industry. Some crews do it a little, some do it a lot. Why? Poor technique, and maybe as a coping method for finishing over-accelerated plaster?

(9) How soon should a pool be filled with water after it is trowel finished?

Research has shown that, within reason, the longer new (fresh) plaster hardens before the pool is filled with water, the better. As long as environmental factors such as high heat, low humidity, excessive wind, etc. are not an issue, it is best to allow 6 to 24 hours of drying after final troweling of the plaster before adding water to the pool.

Unfortunately, it has become the practice of some plastering crews to turn on the water to fill the pool before they leave the site, often within 30 minutes of final troweling. This is detrimental to the surface. Worse yet is the practice of spraying down a pool just after final troweling, just prior to filling, which unfortunately, is occasionally done by plaster crews. This is similar to adding water to the plaster surface during troweling.

These practices only serve to increase the porosity of the plaster surface, making it more soluble, which decreases the long-term durability of plaster surface.

(10) Research lab reveals soft spot cause

In 1999, onBalance retained the cement research firm of R.J. Lee Group to investigate the cause of pool spotting. R.J. Lee was selected because they had performed earlier studies on pool plaster spotting (spot etching) for members of the NPC.

The R.J. Lee group investigators were Dr. Boyd Clark, who holds a Ph.D. in materials science, and Niels Thaulow, who is an expert on aggressive attacks on cementitious materials, and who has research experience relating specifically to swimming pools.

Over a five year period, we provided about 10 samples of actual spotted pool plaster (not coupons as the NPC falsely claims in trying to discredit our work) from various swimming pools to the R.J. Lee Group for analysis. In each case, they determined that the affected “spot areas” on plaster surfaces are high in porosity – a condition they associated with excessively high calcium chloride contents (a hardening accelerator), late and excessive hard troweling, and excessive surface porosity, possibly caused by water used while trowel finishing the plaster surface. These practices lead to the visible soft spots (incorrectly referred to as spot etch) developing later after the pool is filled with water.

(11) What does aggressive water do?

It is known throughout the cement and concrete industry that aggressive water (as defined by the Langelier Saturation Index) will uniformly etch cement-based construction materials. There is a huge body of information about etching already available.

The cement analysis firm of R.J. Lee has now studied pool plaster that had been lightly etched, moderately etched, and heavily etched by aggressive water, to verify whether pool plaster would be affected the same as other cement-based materials when etched.

As a result of their analysis, they concluded that pool plaster fares the same as other cement-based concretes when exposed to aggressive attack, and that established science relative to other cement-based products may appropriately be applied to pool plaster.

The “hallmarks” of aggressive attack which they identified, and that would be present on plaster, included aggressively etched cement paste, etched aggregate (marble sand), and chemical, compositional changes to the cement paste surface. Also documented was that the etching occurred in a uniform and consistent pattern across the plaster surface, not in isolated spots surrounded by non etched cement paste.

(12) What doesn’t aggressive water do?

As mentioned in the last update (#11), R.J. Lee determined that common information about aggressive attacks on concrete is also applicable to pool plaster. Since that was established, we asked them to look again at the spotted plaster they had analyzed in the past, to see if the soft spotted plaster they had studied showed any signs of etching (aggressive attack).

R.J. Lee examined the samples of the spotted pool plaster looking for those “hallmarks” of aggressive attack and determined that no such aggressive etching was evident on the surface of the plaster. The cement surface paste was in good shape, the aggregate on the surface had not been etched and was completely intact and unaffected, known chemical paste disruptions were absent and the classic spot pattern was not consistent with the uniform etching seen in aggressively attacked plaster. This means that using the term “spot etching” is an incorrect description of the plaster spotting problem.

If you wish to review in detail the “etching study” that was co-funded by the San Fernando Valley Chapter of IPSSA, then click on the following web-site link: Etching_Study.aspx

(13) Can etching make spots?

Can aggressive water, in the form of low pH/low alkalinity/low hardness make soft spots? Or any other kind of spots? The answer from the research is a resounding NO… unless there is something defective about that spot to begin with.

Aggressive water is not smart enough to direct its attack against any one spot or area…it has neither brain nor agenda. It etches “good” plaster uniformly. Aggressive water will, however, etch softer and weaker parts of the surface faster than harder, denser parts – so defective soft spots are exposed faster in aggressive pools, slower in balanced pools.

Something to consider: Did you ever wonder why pools that were acid started, acid washed, or NO-drain acid(R) washed by many service techs (and even pool plasterers) have no more spots than pools that did not receive this kind of aggressive treatment? Hmmmm…

(14) Can the same plaster be both spotted and etched?

We have pointed out that, by consensus definitions, soft spots (also known, improperly, as spot etching) occur in smooth plaster. The many studies done by our research laboratories were done on plaster cut out of pools that were smooth. (You can see our case histories, complete with lab reports, for free at onbalance.aspx)

However, the question arises, can there be spots and etching on the same plaster? The answer is, of course! It is quite possible to a have defective plaster that results in the classic soft spots, which is also etched by poor (aggressive) water balance. In that case, the spots will co-exist with rough surrounding cement paste – or the entire surface could be so badly etched that the spots may be etched away and disappear!

But the fact that spots can be (and usually are) found on smooth plaster shows us that they are not caused by aggressive attack.

(15) The Solubility of Plaster

Hard, finished pool plaster is made of many things, including cement and marble aggregate (sand). Even the cement has many components, including some that would obviously be very hard and insoluble (such as silicates and aluminates) and some components in cement that are relatively soft and soluble (such as calcium chloride and calcium hydroxide). Calcium chloride (CC) is the additive that plasterers add to accelerate the hardening of the cement (plaster), and calcium hydroxide (CH) is a byproduct when water is mixed with cement and begins to harden.

It requires aggressive water to dissolve silicates, aluminates, and the marble aggregate (sand); however, balanced water and even positive Saturation water will dissolve CC and CH from the surface of the plaster. In fact, it is CH from the plaster that dissolves from the plaster and becomes “plaster dust” in new pools.

Fortunately, if the plaster is dense and allowed to harden sufficiently before the pool is filled with water, most of the calcium hydroxide on the plaster surface will not be dissolved away and into the pool water. Instead, most CH at the surface is chemically transformed into harder and less soluble calcium carbonate by reacting with bicarbonate (alkalinity) and carbon dioxide in the pool water. This conversion makes for a more durable surface. How do you know that conversion has happened, and is complete? No more plaster dust….

(16) Some plaster surfaces are more porous than others.

What happens if a plasterer adds too much calcium chloride, uses too much water in the mix, scrapes aggregate at surface by over-late, over-hard troweling, and/or adds water to the surface while finishing? These practices make the surface more porous than normal, with more soluble components at the surface. The result: a defective surface with pathways or channels where water can reach – and leach – soluble components (calcium chloride and calcium hydroxide) that shouldn’t be there or shouldn’t be accessible.

This detrimental effect (creating porosity) is compounded by filling the pool immediately after troweling (sometimes even spraying the plaster down with water), and not allowing the plaster to properly and adequately harden before submersion in water. The result: a surface from which even balanced water can leach some of the soluble material from the surface, which over time, begins to look (under magnification) like a very porous sponge.

What’s left on the surface? Aggregate that is not etched and the less soluble and harder components of cement. The higher porosity is why these areas look lighter in color while the surface is still smooth to the touch.

(17) Summary of R.J. Lee Group Studies

To date, we have presented the basic principles behind the cause of pool plaster spotting now known as soft spots, and pointed out why this spotting problem should no longer be called “spot etching.” We have also have provided an analysis, backed by many studies of actual spotted pools from R.J. Lee Group (a cement failure-analysis laboratory) that confirmed these basic principles about the causes of the soft spots which occur in some new swimming pool plaster pools.

The summary is that the spots are excessively porous, and that they have been leached of some of the soluble components. In addition, some of the remaining paste has been chemically reconstituted. The primary points of initiation, or starting points of the spots, have been shown to be associated with aggregate at the surface. All of the spotted pools studied by R.J. Lee had levels of calcium chloride that were at or above the 2% industry-accepted maximum.

Finally, R. J. Lee confirmed that none of the pool plaster studied had been subject to aggressive water chemistry attack.

Another study, www.poolhelp.com/oB-00018.pdf, was the one analysis done on a sample coupon that spotted, rather than an actual pool. This was the coupon made by plasterers at their annual NPC Convention.

All of our studies are available to read for free on our web-site. The case histories include onBalance’s analysis as well as the official reports from the laboratories.

So where did we go from there? It was time for peer review and corroborative analysis… time to call in another professional lab.

(18) Independent Confirmation of Studies

onBalance project ob-00015 was yet another case where a pool spotted, and where the plastering company claimed that the problem was a result of aggressive water. Again, as with previous cases, the plaster was so smooth to the touch that neither we, the home owner, the inspector from the state Registrar of Contractors could locate the spots by touch with closed eyes.

This time, two samples were cored, within inches from each other. One core was sent to R.J. Lee Group, and the other core was sent to Construction Technology Laboratories (CTL), the subsidiary laboratory of the Portland Cement Association. This time, two professional labs studied the same plaster and came to the same conclusions. All three labs (including onBalance) found the calcium chloride content to be around 5%! (Remember, the accepted maximum is 2%)

The R.J. Lee conclusion was consistent with their previous studies; however, CTL provided a few additions in their analysis. In addition to confirming and agreeing with the findings of R.J. Lee, CTL described the spots as highly porous “soft spots” on the plaster surface. We will show in future updates that this terminology is consistent with American Concrete Institute documents, in both language and description of cause.

Second, Laura Powers, who was at the time the chief microscopist for CTL also developed a “model” or causative sequence of events of the creation of these soft spots, which typically begin to show up several months after a pool is filled with water. As did RJ Lee, CTL cites improper workmanship issues, such as late and excessive hard troweling, using excessive water, and calcium chloride abuse as the causes.

You can review this report on our website at oB-00015.pdf.

(19) NPC/Cal Poly and Chemistry

We have been repeatedly asked to comment in these updates on the National Plasterers Council’s (NPC) research project. Although we have written up a more formal critique, and a summary for our website, we can take a short detour and share a few comments before we get back to the valid science.

The NPC, together with California Polytechnic State University at San Luis Obispo (Cal Poly) is performing experiments on swimming pool plaster. “Phase 1” of this research has now been completed, and “Phase 2” is underway. Although the experiment is still in what they call “preliminary” stages, actual conclusions have already been announced in the trade press – making those conclusions, and the supporting data, fair game for critique.

Here are some short, key issues one could ask about the project (as we have, although no attempt has yet been made by the NPC or Cal Poly to actually answer the questions…).

First, let’s talk about the chemistry. As part of the experiments, members of the NPC formed plaster coupons, and gave them to the Cal Poly researchers. Cal Poly placed them in water, and announced in their report that they targeted specific chemical ranges in which they intended to maintain that water. Those ranges followed common pool industry guidelines.

Here are their published pH, alkalinity, and hardness graphs. We have added the yellow shaded bands to denote the announced target ranges.

How well did they do? It appears that in all three categories, the water was out of range over 50% of the time! What is bizarre, however, is that not only did Cal Poly publish definitive conclusions based on these readings, but they determined that water chemistry was the most important “player” in the etching problem!!

How can you base conclusions on data that was more wrong than right? Is this science? Should our industry accept this type of research?

(If your email will not display these graphs, check them out at npc_cal-poly.aspx. )

(20) NPC/Cal Poly, Calcium Chloride and Fill Delay

We have indicated in previous updates that allowing plaster to dry for 6 or more hours before filling a pool lets the plaster harden more, and makes the plaster more durable and dense. When conditions permit, 24 hours is even better. Filling a pool too soon allows water to dissolve more of the weakest or most soluble parts of the surface.

Adding calcium chloride (CC) set accelerator speeds up some of the chemical reactions and causes the plaster to harden much faster, allowing pools to be done faster. However, it is known science that accelerating cement with CC also weakens the product in the long term by creating more porosity, shrinkage, and discoloration. (This fact is not mentioned in the Cal Poly report.) A little CC (less than 2% dihydrate by weight to the cement) is generally allowed as acceptable – but exceeding that amount is not.

In an effort to evaluate the effects of CC in plaster, NPC/Cal Poly did a curious thing. They built 4 test pools, divided them in half, and in the morning, they plastered one-half of each test pool using 2% CC. At midday and later, they plastered the other halves with no CC. Later that day, they filled all of the test pools.

Which halves are going to hold up best? Obviously, the halves that hardened longer before being put underwater would turn out best. For meaningful results, the halves that were accelerated with CC should have been plastered last, not first!

To accelerate the plaster that was done in the morning, and plaster the slower-hardening half several hours later, and then fill both sides of the test pool at the same time… and then announce to the industry that accelerating plaster with calcium chloride proved beneficial is an unfair comparison and obviously wrong. Why would they do that?

(21) NPC/Cal Poly & Using water

The Cal Poly researchers claimed “that the addition of supplemental water (during troweling) does reduce the overall etching deterioration” of the lab samples evaluated. Also, for the test pools, the study states that it “did not reveal any significance of the addition of supplemental water during finishing (troweling).” (Pages 62, 63, 83, 84 in the Cal Poly report)

Have the Cal Poly researchers considered that occasionally, a pool plaster crew may have a fast accelerating (hardening) plaster surface because they added too much calcium chloride (more than 2%) to the plaster or because the weather was really hot or dry? The finisher would have to add lots of water and work it into the plaster to extend the workability time. Obviously, this would be detrimental and would compromise the surface significantly.

Since the Cal Poly study claims that there was not any significant difference between adding water and not adding water, we suspect that only a small amount of water was used when troweling the Cal Poly test pools and coupons.

The NPC was asked if the plastering of the test pools and sample coupons was videotaped so one could see how much supplemental water was used, whether it was excessive or minimal. Their response? There was no need to videotape the plastering and troweling process.

Other qualified entities, such as the Portland Cement Association and the American Concrete Institute, however, are already on record as saying that adding water to the surface during finishing operations is detrimental to Portland cement-based products, and can lead to problems such as dusting and soft plaster. Qualified laboratories such as RJ Lee and CTL are already on record as saying that supplemental water additions are harmful specifically to the pool plaster they have analyzed. Who has more credibility at this point?

(22) Comparing test pools to plaster coupons

The Cal Poly study indicated that the test pools suffered more “etching” deterioration than did the plaster sample coupons. However, the Cal Poly study does not explain why the apparent difference. We can suggest a couple of possibilities:

First, wouldn’t troweling and finishing operations become a focus regarding this aspect? It is very difficult to trowel coupons exactly the same as a pool surface.

Second, was the chemistry of the pool water, which was not published in the report, radically different? They only reported the chemistry of the coupon tanks – and as we have documented, that chemistry was more off target than on.

How can valid conclusions be reported in a scientific document regarding the supposed aggressive chemical effects on the test pools without reporting the readings of the water balance? Especially in light of the poor performance reported in maintaining the coupon test tank's water balance? (Page 82, 83 in the Cal Poly report)

(23) Cal Poly & Chlorine Chemistry

Another conflicting aspect of the Cal Poly study involved their measurement of chlorine residuals in the coupon test tanks and the subsequent analysis on free chlorine. (Page 42 & 43 in Cal Poly report)

Let’s first establish that when chlorine is added to water, it forms HOCl (free hypochlorous acid) and OCl- (free hypochlorite ion). The ratio of the one to the other is pH dependent. Note that both of these forms of chlorine constitute and are “free” – which means “not combined with ammonia.”

This is elementary chemistry, contained in entry-level pool service tech educational material. However, in the Cal Poly report, the researchers reprint a chart from Palin’s “Chemistry and Control of Modern Chlorination” and mislabel the chart. They claim that OCl- is not actually free chlorine at all, and that therefore the pool industry test kits must not work correctly when it comes to free vs. combined chlorine.

Just like the mother who exclaims that her son is the only one in the marching band that is in step, Cal Poly has announced that they know chlorine chemistry, and that Taylor test kits don’t read chlorine right! Shouldn’t Cal Poly wonder what’s up when they are swimming so noticeably upstream?

Then, after claiming that test kits are faulty, Cal Poly, (without documentation or references), states that “a high free concentration of hypochlorous acid (which they refer to as being the only free chlorine) is directly connected to discoloration of pool materials and could initiate etching deterioration.” (Page 43 of report) On what basis does Cal Poly make that statement?

(24) NPC/Cal Poly and Definitions

We have made a point in earlier updates to make sure we properly defined the problem (soft spots, spot etching, or general etching deterioration) so we would be “comparing apples to apples” – not oranges. It doesn’t do any good to argue a point if both sides don’t even agree what the point is!

Soft spots (or spot etching), as defined in the last version of the NPC Technical Manual that everybody agreed on (1998), are from pencil eraser to dime sized.

Here is a picture from that manual, showing dime sized, classic spots.

Did the Cal Poly study look at the same thing? The spots they show in the printed study are almost microscopic – in the test they even state that they had problems counting so many spots in a 3X3 inch square surface! Look at the picture on the cover of their report – the main spot is only about 1000 microns, or about 1/16th of an inch across!

Is this comparing apples and apples, nor not?

(25) NPC/Cal Poly Critique of onBalance Research

You have read our commentary on the NPC/Cal Poly research. We hope you will have noticed that we commented on the available facts – not on the character of the Council nor the researchers. Review is a normal and necessary part of investigative research, a process welcomed by honest and inquisitive interests.
We have reported to you that onBalance has investigated at an “official” level some dozen spotted pools, and hired two separate professional forensic cement/concrete research facilities to aid in those investigations. We have pointed you to where on our website you may view and study for yourself those investigative reports at no cost.

You may ask, as some have, “What has been the corresponding review of the onBalance/RJ Lee/CTL research on the part of the NPC and/or Cal Poly? Here are some quotes garnered from the industry media and the NPC web-site:

“(Our research) is a primary focus of the (NPC) council because there has not been independent, third-party research conducted on the issues that affect the plaster and service industries.” (Mitch Brooks, NPC Executive Director - PSN 2/28/05)

“BEWARE OF FALSE ASSUMPTIONS! There are those critics who are publicly discrediting this (Cal Poly) research trying to advance their own viewpoints. We do welcome constructive questions and professional review. We highly encourage you to research the facts of both sides of any arguement (sp) AND the qualifications of the two entities. Since the publication of Cal Poly’s first protocol conclusions, no one has posed questions to the research PhD’s through Cal Poly or NPC. There are even some industry members who give the perception they are a research lab or institution when they are simply service guys.” (NPC Web-site)

“We don’t know the qualifications of the authors of the (onBalance) letter, so we do not wish to comment on the validity of their “own” studies. However, unbiased and publicly acceptable research is typically conducted at reputable academic institutions. Research methodology and approach are even more important than the research topic.” (Letter to PSN 1/17/05 by Professors Kachlakev and Pal)

“The NPC is no longer combating those who would like to place ALL the blame of pool surface problems on plasterers. We are not looking to place blame on anyone.” (Mitch Brooks NPC - Service Industry News 1/31/04)

“The (onBalance) seminar on plaster problems was of course way off base, and we’ll just let our Cal Poly Research Program present their conclusions in July which the NPC will live by. Of course, the question is, will onBalance live by Cal Poly’s findings?” (Mitch Brooks NPC May-June 2004 newsletter)

(OnBalance’s response: If the research is done correctly, and with appropriate conclusions, then the answer is yes).

“The few individuals who are creating the conflict between the service industry and NPC are not skilled at pool plastering – which they readily admit. And what they have done in my opinion is no different than a legal aide putting out a sign saying “Attorney at Law!” (Mitch Brooks – NPC Jan/Feb 2004 newsletter)

(Note to readers: Actually, Kim Skinner, a member of onBalance, is a former pool plasterer).

“I think it is interesting that people are listening to the critics (onBalance) who have no experience in plastering. They come out of nowhere and put up a placard and say they are a research entity. I am wondering why people are actually listening to these guys preach what they preach.” (Mitch Brooks PSN 2/13/04) See note above about Kim, and we have hardly “come out of nowhere” – you may review our industry experience at www.poolhelp.com/onbalance.aspx.

In regards to those who disagree with the conclusion given in the Cal Poly study that aggressive water causes “spot etching” or soft spots, Alan Smith in PSN 9/3/04 said, “You will always have the naysayers and people protecting their own interests. You can prove it beyond a reasonable doubt and they still won’t buy into it. We can’t worry about that.”

You may ask yourself:

• Why the above quotes by NPC people are ad hominem (Arguments against us instead of against the actual issues raised in our research itself),
• Why the NPC consistently refuses to engage us on the facts as established by both us and by the qualified research institutions we have engaged.
• And if the NPC and/or Cal Poly have really proved anything “beyond a reasonable doubt…”

Those would be good questions.

(26) Cal Poly Review

One could assume that, rather than respond directly to onBalance’s research, the NPC chose to respond by doing research of their own and releasing it. If so, let’s quickly summarize what Cal Poly studied and what conclusions they released.

• The study does not address the consequences of using too much water during finishing, and the amount of water used and the technique was not video taped nor documented.
• The study does not address the consequences of late over-hard troweling, nor did it document the amount of hard troweling performed.
• The study incorporated a fatal methodology flaw by not allowing the non-accelerated (without calcium chloride) plaster to harden sufficiently before being submerged in water while giving the accelerated (2% CC) plaster an additional five hours to harden. The study does not address the abuse of calcium chloride i.e., using more than 2% CC. Cal Poly then announced the “importance of calcium chloride” to plaster and that it reduces etching!
• The undocumented water supplementation and hard troweling were both performed by the NPC - in spite of assurances that the research was independent.
• The study does not properly address water chemistry because the targeted ranges were not maintained, yet the researchers released conclusions based on this parameter.
• There is no assurance that the research investigated the same spotting phenomenon, since the definition given by Cal Poly does not match the definition used in the industry.
• NPC/Cal Poly has also renamed the spotting phenomenon without any justification given for why the two phenomena (generic general etching vs. spot “etching” or soft spots) should be referred to by the same term (“etching deterioration”).
• Existing science (in the form of ACI and/or PCA studies and guides) relating to admixture effects and effects of finishing practices is not only ignored, but contradicted.
• Access to the data of the study has been restricted: a large fee for the report, and no access to the data that is missing from the report.

A member of the NPC research committee, Dan Gossage (from IPSSA) incorrectly announced that the study determined that excess calcium chloride, hard troweling, and water supplementation “had little or no effect on etching.” As we mentioned above, the Cal Poly study did not address these issues that onBalance has identified as contributing to the creation of soft spots on plaster.

In light of these facts, we don’t feel that the NPC/Cal Poly research or the attendant report constitute any form of rebuttal to the facts we have presented. Our questions to them have been met with a refusal to respond to us.

(27) Other Pertinent Experiments

Some interesting research projects have been performed in the pool industry during the 1990’s, which, in various ways, have shed some light on the plaster spotting issue.
In 1999, when Doug Latta and Que Hales (of onBalance) were on the NPC Research Committee with other pool plasterers, a joint experiment was devised. The NPC would make two sets of sixteen plaster sample coupons, each one foot in diameter and about one-half inch thick. Each of the sixteen coupons was comprised of a different cement and aggregate make-up.

Each of the sixteen hardened coupons was cut up into quarters. In two different locations (Que Hales in Tucson and Kim Skinner in Livermore), four water tubs were prepared – all four containing tap water, and all four with a pH of 7.5… but with the alkalinity levels in the four tubs were adjusted to 40, 80, 120, and 160 ppm respectively.

One quarter of each coupon was placed into each of the tubs – so each full coupon was being exposed to water of the same pH but four different alkalinities. This water submersion and maintenance at their respective chemistries lasted for 8 months.

After 8 months, the quartered coupons were removed from the water barrels, reassembled, and inspected. A strange thing was noted about one coupon - it had developed spots on all four quarters or in other words at all four alkalinity levels. Furthermore, the spots appeared only on the troweled side of those quartered coupons, but not on the molded side (which was not troweled) although those molded sides of the coupons were also subjected to the same water conditions as the troweled side!

The onBalance write-up and the RJ Lee analysis of this coupon may be reviewed at http://www.poolhelp.com/oB-00018.pdf.

Although the NPC later disassociated themselves with this experiment, and declined to discuss it, we can still learn some key points from it:

• The coupon contained more that the 2% high end limit for calcium chloride.
• The coupon spotted at alkalinity levels of 40, 80, 120, 160 ppm. In other words – alkalinity was not a deciding factor on whether or not the plaster spotted.
• The coupon spotted only on the troweled side – even though the molded side was exposed to the same water.
• The differences between the troweled and the molded sides include no hard troweling and no added water during finishing.
• Upon examination, RJ Lee found the plaster spotting to be consistent with spotting in actual pool samples

Pictures of these coupons and the experiment may be viewed at http://www.poolhelp.com/NPC_TA_Coupons.aspx

(28) The Arizona test pool experiment

Plasterers conducted several research experiments in the 1990’s to determine the cause of “spot etching” or plaster spotting. One was a test pool in Phoenix Arizona, performed by the “Arizona Plasterers Council.”

In 1990, this test pool was plastered with eight different plaster sections comprising of different combinations of cement and aggregate brands. This test pool was maintained with balanced water for a few months and then aggressive water the remainder of the year.

After one year, the plasterers inspected the pool and announced that there was spotting in all eight sections. They also claimed that aggressive water was the only common denominator, so it was what caused the spotting to appear.

A year later, onBalance, with a member of the trade press, looked at this pool. We all noticed a few things that the plasterers had not shared. Some sections had nearly 80% of the plaster surface covered with spots, but one or two sections had only about 20% of the surface covered in spots with large areas completely unaffected! Also, the patterning of the phenomenon varied from section to section – and at least some of the patterning was directly attributable to troweling patterns!

In later NPC meetings, when plasterers referred to this test pool as “proof” of an aggressive chemical cause for spotting, they were asked why the difference on the amount and patterning of the spotting from one section to another, and how and why could water affect each section so differently? If water chemistry was the sole reason for the spotting, wouldn’t it affect all of the plaster sections consistently? The plasterers were also asked how much calcium chloride (CC) was added to each plaster section. They would not respond to our questions.

A few images captured from the video are on our website, although the capture quality isn’t the best: http://www.poolhelp.com/NPC_AZTestPool.aspx.

What can we learn from this experiment?

• Since none of the video footage provided to the industry shows whether the plaster sections were late hard troweled and/or wet troweled, and since chloride analysis was not provided, this test pool does not disprove the RJ Lee/CTL spotting scenario.
• Since excess calcium chloride, excessive late hard troweling and wet finishing may have also been “common denominators,” this experiment did not prove causation from water chemistry only.
• Since the severity and the patterning of the spotting varies greatly from section to section, and were each finished by different plastering crews, workmanship practices are possibly the reason for the variation.
• Since specific, crucial details are being withheld from the industry, there is more to be learned if the plasterers involved would become more open and cooperative.

(29) Pasadena Test Pool

In 1991, another test pool was plastered by NPC members, this one in Pasadena.
This pool was also subdivided using tile into eight different plaster sections. Different combinations of cement, aggregate, calcium chloride, and finishing crews were used in the different sections.

The test pool was acid started, and then maintained with balanced water for about eight months, followed by aggressive water for about four months. The chemical care was provided by Stan Zielinski (an IPSSA member).

The pool was then inspected by the NPC. They noted that only two sections out of eight had spots (spot etching). None of the other sections had any spotting.

So what did the NPC announce to the industry about this pool? Nothing. Neither the NPC nor the involved plasterers released results of this test pool. They never addressed the interesting facts that indicated something other than water chemistry as causing a few spots to develop in two plaster sections out of eight.

In 1997, about five years later, onBalance went to look at this pool with Stan Zielinski. Stan was very forthcoming about the pool and his experiences and opinions derived from it. We noted that still only two sections had spots. None of the other six sections of plaster had developed any spots (although one of the other sections had 18-20 calcium nodules). This information was brought to the attention of the NPC, and we asked for a response about their position regarding these results. The NPC refused to address any of the results of this test pool.

We asked Stan for a written analysis of his experiences and opinions, which he provided.

Is there a legitimate reason to not conclude anything from these experiments, and allow the results of this NPC experiment to be ignored and discarded?

(30) NPC Technical Manual & Spot Etching

Prior to the release of the NPC Third Edition 1998 Technical Manual, the manual revision committee, which included Que and Doug from the service segment, spent a lot of time specifically deciding how to handle the “spot etching” issue within the tech manual. The prior Technical Manual had not addressed this issue.

The committee members reviewed all the available material in an effort to assign a causative factor and a responsibility statement. The plasterers felt that aggressive water was the cause, and the service people felt it was a materials and/or workmanship caused problem. They reviewed material included the Arizona test pool (1), the Pasadena test pool (2), the Dow Whitney report (3), many articles from the trade press, and some independent reports.

After much debate, both sides agreed that, although symptoms of the problem could be described, no one at that time could conclusively, with scientific support, assign causative factors or responsibility.

The resultant text, which was approved by the committee, and later ratified by the NPC Board of Directors, included the following text:

“Spot etching is associated with the dissolution by water of calcium hydroxide from the pool plaster matrix although the cause for the random nature is not clearly known. No theory has been proven or unilaterally accepted. Until the actual causative factor(s) for spot etching can be identified, no responsibility can be assigned.”

After the release of the 1998 Technical Manual, a series of things happened:

• In 1999, the Alkalinity Coupon Experiment (4) indicated that chemistry could not be the cause of spotting
• In early 2002, the etching experiment (5) provided proof that “spot etches” were not actually etching at all
• In early 2002, the service industry members of the technical manual committee (other than the IPSSA liaison) were ejected from the committee.
• The newly constituted technical manual committee asked for input on the new version. onBalance provided them with a case history (6) showing that spotting is a result of workmanship.

Then, the 2002 version of the Technical Manual was published in January 2003. The picture and text of spot etching had been removed. A glossary item had been added:

Spot Etching – A slang term used in the swimming pool plastering trade that denotes the deterioration of the surface of a cementitious coating by chemical attack. See also Etching Deterioration.

Amusingly, the front of the manual also contains the statement:

“Unsubstantiated theories” which do not have significant scientific data to support their position, or any conjecture that serves only to mislead the general public, will not be considered herein.

Who is “misleading” whom?

Formerly and industry consensus document, this version of the manual has not been accepted by IPSSA, SPWTP, or the CSLB.

(1) http://www.poolhelp.com/NPC_AZTestPool.aspx

(2) http://www.poolhelp.com/NPC_PasadenaTestPool.aspx

(3) http://www.poolhelp.com/whitney_letter.aspx

(4) http://www.poolhelp.com/NPC_TA_Coupons.aspx

(5) http://www.poolhelp.com/Case%20Report%20-%20Etching%20Study.pdf

(6) http://www.poolhelp.com/oB-00004.pdf

(31) NPC Technical Manual & Calcium Chloride

Two final emails on the tech manual and we'll be getting back to the research we have done with our labs...
So the next question would be: what position is taken in the new NPC Technical Manual on two of the issues that we have raised, namely overuse of calcium chloride and using water while finishing a surface?
Section 2.5.1, discusses the use of calcium chloride and section starts out by saying that “Calcium chloride should not exceed 2% of the weight of cementitious materials…” It then states that the 2% limit was borrowed from the concrete and stucco trade, and that the reason for the limit is that calcium chloride can deteriorate metal reinforcement in concrete or stucco. They then note that “pool plaster has no metal reinforcement imbedded within it.” As a result, the NPC states that their 2% limit position “is based on insufficient knowledge or experience to determine the benefits, or the detriments, of adding greater amounts.” Continuing, the manual says, “In short, the 2% limit on calcium chloride may not be critical to swimming pool plaster.”

In debate, this is called a “straw man” tactic – redefining the issue in terms that you can successfully argue, while ignoring the real issue. What are the real issues regarding calcium chloride use in pool plaster?

• It causes graying discoloration in white plaster. The more that is used, the more discoloration.
• It causes discoloration and blotchiness in colored plaster.
• It makes the cement paste less dense, or more porous.
• Excessive amounts cause shrinkage, cracking, and can even backfill void spaces with reaction byproducts – a potential cause for spalling or peeling.

The Technical Manual then states that it is well documented that calcium chloride between 1% and 2% is shown to provide beneficial properties of increased strength, increased density, will lower porosity, and increase watertightness at early ages!

Although it is true that calcium chloride will increase the early strength of cement much faster, especially in cold temperatures, long-term strength can be decreased, especially when using too much calcium chloride. Also, we dispute that calcium chloride will lower porosity – there are many studies in the cement/concrete industry literature that show calcium chloride increases the shrinkage of cement, and thus increases porosity.

The NPC was given a study by onBalance in 2004 that indicated that nearly 20% of all calcium chloride used in plaster will be leached out (by balanced water) and dissolved into the pool water within days of being submerged. Since some of the original material is then missing, leaving “space” behind, this therefore indicates an increase of porosity with increasing chloride content, not a decrease. Apparently, the NPC ignored this.

Where are these studies the NPC is relying upon for these supposed beneficial claims of using calcium chloride? Is it from the Cal Poly study? If so, we have shown that the methodology used to show that was flawed. And while we’re at it, why aren’t the long-term effects of calcium chloride abuse discussed in the NPC manual’s section on Long-Term Deterioration?

(32) NPC Tech Manual & Water Use

In this last update on the Technical Manual (before we return to the research data we want to share), we need to mention the importance of the right amount of water when using Portland cement.

The cement and concrete industry, as represented by the Portland Cement Association (PCA) and American Concrete Institute (ACI), sets a limit on the amount of water to be used when mixing and making cementitious products. This limit is half water by weight to the weight of cement, which is called a .5 water-to-cement ratio. This is especially for cement-based materials to be employed in a water environment - in order to limit water permeability.

The new Fifth Edition 2005 NPC Technical Manual does not set a limit on water content other than to say not to over-temper (add too much water to) the plaster mix. But the Tech Manual allows more re-tempering water to be used when extreme conditions are present, such as high temperature, high winds, and high evaporation.

Also, the PCA and ACI advise against sprinkling water (for the purposes of lubrication) onto the surface while troweling. In fact, they also advise against troweling a cement surface while bleed water (water which has risen to the surface through settlement of the sand and cement paste) is on the surface of cement products, since any process which skews the water-to-cement ratio on the surface will increase porosity and weaken the cement surface, leading to crazing, spalling, and dusting. The NPC Tech Manual, on the other hand, actually states that the use of lubricating water is an acceptable practice and commonly used within the pool plastering trade… but then follows with a qualifier, “If used improperly, lubricating water can be damaging to the upper surface of the coating surface.”

As a side note, the Cal Poly study claimed that using different amounts of water in plaster didn’t have any effect on etching. However, the Cal Poly study used a .425 and a .5 water-to-cement ratio, both within approved limits. That research phase did not actually study or address higher than approved water cement ratios.

As we return to our research, and the Construction Technologies Laboratories plaster spotting model, we will see that these practices are factors leading to the spotting problem.

(33) Assembling the Puzzle Pieces, Step 1

Based on the research onBalance has performed, backed by the expert analysis of RJ Lee Group and Construction Technologies Laboratories (CTL), the puzzle pieces for plaster spotting have been assembled. These pieces have been identified as excess calcium chloride (typically noticeably over the 2% industry standard), excess water (primarily wet finishing techniques, although excessively wet mixes and premature filling seem to also potentially play a role), and late excessive hard troweling.
(We would like to reiterate at this point that current indications are that it typically requires all three of these factors to excess to generate the spots – moderate amounts of calcium chloride, wet finishing and/or late hard troweling appear to be insufficient to create the effect.)

So next, let’s put the pieces of the puzzle together in sequence, as described in the CTL model. To do so we are going to use a graphic depiction. On the left is a scanning electrical microscope (SEM) cross-sectional scan of a piece of pool plaster. The large grey things are individual grains of sand. The “speckled” filler is the cement paste. To the right is a graphic we will use for the illustration, which is based on the SEM below.

In the next few email updates, we will illustrate the CTL model using this picture, and we will include the specific text (from CTL, RJ Lee and other sources) supporting the step-by-step progression.

As we go through this sequence, there are a number of questions you have asked that we hope to answer, including:

• Why do the spots have a piece of sand in the center?
• Why do the spots start small, and then “grow”?
• Why are the spots generally round?
• Why can the effect follow the edge of a crack, tile line or plastic fixture?
• Why are the spots sometimes tan or aqua instead of white?

(34) Assembling the Puzzle Pieces, Step 2

The first transition occurs when excessive amounts of calcium chloride set accelerator are added, causing shrinkage (see references below). Of course, CTL’s Chief Microscopist Laura Powers noted, the aggregate (sand) doesn’t shrink – but the cement paste does. This leads to a pulling away of the paste from the sand.

References:

“Accelerators such as calcium chloride and triethanolamine result in increased drying shrinkage of concrete.” (Design and Control of Concrete Admixtures Portland Cement Association 14th Edition, 2002, p. 113).

“Calcium chloride addition results in a higher shrinkage at all times (shown in Table).” (Ramachandran, Concrete Admixtures Handbook 2nd Edition, p. 229)

“Calcium chloride is reported to increase creep and drying shrinkage of concrete.” (Manual of Concrete Practice American Concrete Institute – Chemical Admixtures for Concrete 212.3R-13)

(35) Assembling the Puzzle Pieces, Step 3

In addition to the shrinkage that pulls the paste away from the sand, additional micro porosity [1] is formed by the addition of excessive [2] amounts of calcium chloride set accelerator. Although a certain amount of void space and porosity is normal in cement paste, excess acceleration leads to excess porosity [3]. The compositional qualities of the cement paste are also affected, including the formation of byproducts (such as Freidel’s Salt) which are directly tied to excess chloride content [4].

[1] “The network of random micro cracks observed in the plaster is attributed to shrinkage, possibly caused by high paste content and by the addition of calcium chloride (Design and Control of Concrete Admixtures Portland Cement Association 14th Edition, 2002, p. 113).” Report of Laboratory Evaluation, CTL Project No.: 154801, August 14, 2003, p. 4

[2] “Results of chemical analysis… show that the acid-soluble chloride content of the plaster is 1.063 wt%.” Report of Laboratory Evaluation, CTL Project No.: 154801, August 14, 2003, pp. 30-38. Note: This scenario was developed after a review of industry literature, other studies of spotted pool plasters, and analysis of spotted plaster from onBalance Case oB-00015, which may be viewed at www.poolhelp.com/oB-00015.pdf. The chloride analysis is from that pool plaster. As shown in our paper on chloride analysis of hardened pool plaster (www.poolhelp.com/Calcium%20Chloride%20Determination.pdf), this equates to about 6% calcium chloride dihydrate – so this particular pool had about three times the maximum limit of set accelerant.

[3] "Open microcracks are common in the paste in all zones, the cracks abutting aggregates more or less perpendicularly." (Dr. Don Campbell, Campbell Petrographic Services, examining the same plaster as our Case History oB-00005M. See www.poolhelp.com/oB-00005M.pdf )

[4] “The paste appears lacy with patches of calcium-depleted leached paste containing cement relics interspersed between cement threads of fine-grained calcite intermixed with other phases, including Freidel’s salt (calcium chloroaluminate).” Report of Laboratory Evaluation, CTL Project No.: 154801, August 14, 2003, pp. 30-38.

(36) Assembling the Puzzle Pieces, Step 4

When plaster is setting too fast (as from over-acceleration), it needs to be “knocked down” or forced smooth with greater-than-normal force from troweling. As this over-porous, aggregate-loose plaster is late hard-troweled, with some aggregate already flush to the surface, even more aggregate can be exposed through the scraping process [1]. This leads to open pathways from the surface down into the space around the aggregate.

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[1] Petrographers can detect “artifacts” of the late hard troweling process, which can include surface textural phenomena as well as changes in the distribution, size and shape of the void spaces in the paste. Here are some pertinent conclusions from Case History 0B-00004 relating to surface troweling texture, reconstruction of the cement paste, and excess chloride:

• The texture on core #3 is due to troweling performed after the surface is partially set. This “over-troweled” surface texture is a phenomenon caused when plaster, or concrete, is troweled without enough water present in the hydrating paste. Loss of water is caused by evaporation, due to the time between placement and finishing and the ambient temperature. Accelerators added to the plaster mix can enhance this effect by shortening the time available for finishing.
• The same micro-structural features observed by SEM in core #3 are also observed in core #2. These features are caused by the same phenomenon, water driven reconstruction of the hydrated cement paste. In core #3 this reconstruction process corresponds to the initial over-troweled texture. The SEM data implies that the features observed in core #2 are also due to over-troweling.
• The presence of elevated chlorine in the paste in core #1 and #3 implies an elevated amount of calcium chloride was used in the mix. This elevated chloride level may have enhanced finishing problems, specifically over-troweling, by accelerating the set time. (From RJ Lee Group Project No. MAH106172, www.poolhelp.com/oB-00004.pdf p. 18 - underlining added for emphasis. Chloride analysis on this plaster showed 2.5%)

(37) Assembling the Puzzle Pieces, Step 5

When the trowel scrapes directly on an exposed piece of loosened, or compromised aggregate in a very late, hard trowel pass, it can “jiggle” (scientific/technical term ;0) the piece of sand in its loose bed. So now we have overly porous cement paste containing loose aggregate, some of which is exposed to the surface, and some of which has been additionally disturbed through the late hard trowel pass.

(Based on verbal discussions with Laura Powers)

(38) Assembling the Puzzle Pieces, Step 6

When plaster has been over-accelerated, and the finisher is attempting to make it smooth after it is already hardened, in addition to over-troweling [1], some finishers add water to the surface – commonly with brushes or sponges. This is, of course, a violation of good construction practice [2][3], but at this point it has been made necessary by the over-acceleration of the paste. One of the downsides to this water addition is that it results in even more porosity – in addition to any porosity resulting from the chloride acceleration! [4]
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[1] “The discolored regions of the samples correspond to the textured surface... trowel marks are readily apparent in discolored spots.” “These 'trowel marks' may be influenced by the amount of the calcium chloride.” “All of the samples have the same micro-structural feature along the top surface, as observed by SEM, a decalcified region overlaid by a calcium-rich material. These features are caused by the same phenomenon, water driven reconstruction of the hydrated cement paste... this reconstruction process corresponds to the initial over-toweled texture.” (from RJ Lee Group Project No. CCH003627, www.poolhelp.com/oB-00019.pdf p. 18

[2] “One of the most common errors encountered in trying to correct poor workability is to add more water. Adding water upsets the water-cement ratio, reduces the strength of the hardened concrete, and can cause other serious problems.” (Concrete Inspection Procedures, Portland Cement Association, New York:John Wiley & Sons, Inc. 1975 p. )

[3] “The use of additional water applied to the surface by dashing with a brush, sprinkling, or spraying during finishing or edging operations should not be permitted.” (ACI Manual of Concrete Inspection, American Concrete Institute, Detroit:ACI 1981 p. 250)

[4] “Based on the results of the analysis, white discoloration is related to the presence of localized areas of high porosity resulting from the leaching of the paste at and near the surface of the plaster. The apparent high [water:cement ratio] locally may result from secondary hydration of cement that is often seen at surfaces of cement paste exposed to copious amounts of water.” Report of Laboratory Evaluation, CTL Project No.: 154801, August 14, 2003, pp. 30-38

(39) Assembling the Puzzle Pieces, Step 7

This added water settles around the open void space surrounding exposed, loose aggregate – putting water where water is not meant to be, thus artificially skewing the cement:water ratio in the transitional zones between aggregate and paste. [1 through 4]

[1] “The areas of weak paste appear to be centered predominantly over aggregates and cracks. Troweling techniques that expose aggregates at the surface may provide avenues for water to enter the plaster along the boundary between the paste and the aggregate.” (Laura Powers, Report of Laboratory Evaluation, CTL Project No.: 154801, August 14, 2003, p. 4)

[2] “During manual SEM examination of the cross-sectioned affected regions a decreasing porosity from the top to the bottom of the region was observed. Three porosity regions were delineated during the analysis. The water-to-cement (w/c) ratio determination examines the porosity of a given area and converts that porosity into a calculated equivalent w/c ratio.” “Water-to-cement ratio of unaffected paste regions is 0.52.” “Affected region porosity is quite high; equivalent w/c varies between 1.8 and 0.7 (apparent w/c at this time – not initial w/c.” (Dr. Boyd Clark, RJ Lee Group Project #CCH908603 See www.poolhelp.com/oB-00003.pdf )

[3] “Within the dimensions of the cores (ca. 3 inch diameter core sample), the paste of this plaster appears to have variable water-cement ratios throughout each core.” (Dr. Don Campbell, Campbell Petrographic Services, examining the same plaster as our Case History oB-00005M. See www.poolhelp.com/oB-00005M.pdf )

[4] “In these studies, no single factor seemed to cause discoloration. However, combinations of factors caused very severe discoloration. Factors found to influence discoloration were calcium chloride admixtures, cement alkalies, hard troweled surfaces, inadequate or inappropriate curing, concreting practices and finishing procedures that cause surface variation of water-cement ratio, and changes in the concrete mix.” (Surface Discoloration of Concrete Flatwork, Greening and Landgren, Portland Cement Association Publication RX203 – underlining added for emphasis.)

(40) Assembling the Puzzle Pieces, Step 8

As this added and troweled-in water reacts with surrounding, weakened paste and then dries (between the wet troweling and the actual filling of the pool hours later), a very weak, porous, crystalline-lattice paste is left behind, composed primarily of a very soluble complex of calcium hydroxide.

References

Microcracks are unusually numerous in the plaster of both cores, the thin cracks typically abutting aggregates and probably representing autogenous shrinkage of the abundant paste (30 to 35%). One crack in Core D-2 was partially filled with coarsely crystalline calcium hydroxide, suggesting autogenous healing, a process that is only effective in wet paste in the early stages of chemical solidification and hardening. (Dr. Don Campbell, Campbell Petrographic Services, Report page 2, examining the same plaster as our Case History oB-00005M. Bold added for emphasis. See www.poolhelp.com/oB-00005M.pdf )

Microcracks are extremely abundant in the paste of the plaster; cracks are approximately 2 to 3 microns wide and open. The cracks are mainly abutting aggregates, but a few pass through nearly the entire plaster, terminating within 0.2 mm of the base, one of which in Core D-2 passes around almost all aggregates, widens upward to 10 microns, and is filled with secondary coarsely crystalline calcite. The walls of the latter crack do not appear sharp but are ragged, suggesting plastic or near-plastic deformation.” (Dr. Don Campbell, Campbell Petrographic Services, examining the same plaster as our Case History oB-00005M. Bold added for emphasis. See www.poolhelp.com/oB-00005M.pdf ) Note: “plastic” means still malleable – meaning that these deformations, cracking, crystalline formation, etc. happened while the plaster was still hardening, before the pool was filled with water.

Assembling the Puzzle Pieces, Step 9

The pool is then filled with water. As we have previously mentioned, the sooner the pool is filled after troweling, the less time is allowed for the hardening, densifying reactions to take place. So filling a pool too soon is always bad, and filling a pool too soon when it is defective in this manner even worsens the end effect [1]. Spraying down the fresh plaster walls, steps, or floor before the plaster is ready may result in the same types of problems as filling the pool too soon [2].
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Reference

[1] See our article on the effects of the time interval between finish troweling and filling a pool, as reported in Service Industry News, March 15th 2004 (see www.poolhelp.com/SIN_ReprintFillDelayArticle.pdf).

[2] See commentary and pictures in our Case History oB-00017 on our website at www.poolhelp.com/oB-00017.pdf

Assembling the Puzzle Pieces, Step 10

Over time, which may be hours, weeks or a few months, the weak, porous crystalline material is slowly leached [1] from around the exposed surface of the aggregate by water. The first noticeable effect is a whitened halo around the exposed aggregate’s tip, since porosity lightens the color of the paste [2][3].

The length of time required for the spots to begin leaching and then to enlarge is influenced by a number of factors. The primary factor which speeds up the process is porosity. Other “speeding up” factors include aggressive water, and high water flow rates over the surface.

Some of the compounds in the plaster are also just more soluble than others. For instance, calcium hydroxide is about 100 times more soluble than calcium carbonate (and that’s in balanced water), and calcium chloride is about 100 times more soluble than calcium hydroxide. [4]

References

[1] You may recall from email update #3 (www.poolhelp.com/emails.aspx) that leaching is different from etching. Leaching describes the solvent action of water – independent of its chemical balance – just by virtue of there being water present. Etching, on the other hand, describes a chemical quality of water where, because of such things as low pH, low alkalinity, low hardness, etc., aggressive water can dissolve some substances that would not usually be leached.

[2] “Troweling techniques that expose aggregates at the surface may provide avenues for water to enter the plaster along the boundary between the paste and the aggregate. Report of Laboratory Evaluation, CTL Project No.: 154801, August 14, 2003, p. 4

[3] “The white areas seem to form due to local leaching of cement paste creating porous, decalcified areas. The pattern of the leached areas may have been determined by the finishing process, with local areas of higher water:cement being more susceptible to leaching of calcium ions.” Niels Thaulow, RJ Lee Group Project #MAH112353 See http://www.poolhelp.com/oB-00005M.pdf p. 48

[4] See, for instance, Dean’s Lange’s Handbook of Chemistry, pp. 5.11-5.12. So when greater percentages of the plaster are composed of these more soluble materials, not only do they create physical changes that lead to greater porosity, but in and of themselves they are more soluble to begin with. And when they are leached, the “empty space” left behind leads to even greater porosity. So the more chloride in the mix, the greater and the faster the leaching. And the more porous the plaster, the greater and the faster the leaching.

Assembling the Puzzle Pieces, Step 11

Once water has access to the sub-surface paste (where it shouldn’t have unobstructed access…), it spreads laterally through the micro porosity resulting from the acceleration shrinkage [1]. This progression is just under the surface, spreading parallel to the surface, in all directions from the starting point [2]. This results in a small white halo at the exposed point of sand, growing in all directions from that point – thus forming a growing round white spot.
How do we know this is a leaching phenomenon rather than etching? For one thing, the sand is not affected even though it, too, is acid soluble [3] [4].

[1] “Water may also enter the plaster at crack locations and then circulate through microcracks.” Report of Laboratory Evaluation, CTL Project No.: 154801, August 14, 2003, p. 4

[2] “Carbonated, porous regions follow cracks and paste/aggregate boundaries. Visual observations indicate affected regions are associated with aggregate. UV and PLM indicate affected regions follow paste/aggregate boundaries and cracks into the interior (into unaffected paste regions).” Dr. Boyd Clark, RJ Lee Group Project #CCH908603 See http://www.poolhelp.com/oB-00003.pdf Underlining added for emphasis.

[3] “The outer surface of the marble [aggregate] does not exhibit evidence of dissolution or etching.” Report of Laboratory Evaluation, CTL Project No.: 154801, August 14, 2003, p. 2

[4] Angular, fine aggregates were exposed at the surface due to loss of material from the surface. The exposed dolomite aggregate did not show evidence of acid etching.” Niels Thaulow, RJ Lee Group Project #MAH112353 See http://www.poolhelp.com/oB-00005M.pdf p. 48

(44) Assembling the Puzzle Pieces, Step 12

As chloride and hydroxide are leached, the porosity network is enlarged, and a small amount of surface is lost. This leaves a depression that is visible microscopically, but which is not detectible tactilely (by touch) except for severe cases [1] [2].
Since the spots are more porous, they also accept staining from metals in the water easier than denser, intact paste [3]. This often gives the spots a tan or aqua tint.

[1] “Based on the results of the analysis, white discoloration is related to the presence of localized areas of high porosity resulting from the leaching of the paste at and near the surface of the plaster.” Report of Laboratory Evaluation, CTL Project No.: 154801, August 14, 2003, p. 4 (www.poolhelp.com/oB-00015.pdf)

[2] “The microstructure of the paste is disturbed within the area of intense carbonation. The paste appears lacy with patches of calcium-depleted leached paste…” Report of Laboratory Evaluation, CTL Project No.: 154801, August 14, 2003, p. 2 (www.poolhelp.com/oB-00015.pdf)

[3] “The subsequent formation of colored rings appears to be a secondary phenomenon caused by deposition in the porous areas and is related to interaction between water and dissolved salts (such as phosphate), and trace elements (such as copper) in the water.” Report of Laboratory Evaluation, CTL Project No.: 154801, August 14, 2003, p. 4 (www.poolhelp.com/oB-00015.pdf)

(45) Assembling the Puzzle Pieces, Summary

So what does the research show? The same “chain reaction of consequences” we first introduced as a hypothesis in 2000 [1], with fine tuning and documentation.

Plaster spotting has been shown to be the result of:

• Over-acceleration of plaster by the addition of excessive amounts of calcium chloride. This results in an over-porous paste and paste-aggregate separation.
• As a coping mechanism, the plaster is over-troweled, late in the plastic setting phases. This further disturbs aggregate in its too-porous, weak paste bed.
• Also as a coping mechanism, water is splashed or brushed onto the surface and troweled in. This forces water into the porous surface, which, upon drying, leaves a porous, crystalline hydroxide formation in the paste-aggregate transition zones.
• As these compromised pools are filled with water, it leaches the weak zones at the aggregate entrances over time, and then the leaching proceeds laterally in all directions through the excessively porous paste. This is first seen as a small, white round “halo” formed at the tip of an aggregate, and then the spot enlarges in a circular progression from the initiation point over time as the leaching progresses.
• The same process can follow other transitions or entrance points, such as paste-tile, paste-plastic fitting, or craze crack edges instead of initiating at an aggregate.
• The spots appear white, or whiter than the surrounding paste due to the porosity.
• If present, heavy metals deposit in the porous spots, giving them tan or aqua colors.
• Upon analysis, no evidence of acid or aggressive attack is present.
  

There is consensus between onBalance, and the scientists at the PCA’s Construction Technologies Laboratories, and the RJ Lee Group. There is supporting documentation from the Portland Cement Association and the American Concrete Institute, which complements the findings of the two aforementioned labs.

Of course, acid or aggressive chemical attack does ruin pool plaster. We’ve all known that, even without the help of Dr. Whitney at the University of Florida or the present study at Cal Poly. However, plaster spotting is a different phenomenon with different causes and different results.

[1] “A Chain Reaction” Pool & News February 23rd 2000