1	The Effects of Curing and Aggressive Chemistry on Pool Plaster
2	The Experiment One large (1½ by 2 foot) plaster sample was formed with a single batch of material, and troweled as a single unit Cement:water 1:0.5 Cement:aggregate 1:1½ Cement:calcium chloride 1:0.01 (1%)
3	The Experiment After troweling and hardening, the coupon was cut into eight sections and labeled One of the sections was set aside, dry One section was “bicarb” started Water adjusted to TA 350 with bicarb before coupon was added One section was “acid” started Water adjusted to pH 4.5 with acid before coupon was added The other five were “traditional” started Water adjusted to pH 7.5 daily after coupons were added
4	#1 - Dry Coupon This coupon was kept dry for the entire course of the experiment
5	#2 - Bicarb Start This coupon was bicarb started for one week, with a daily pH check (maintained at 8.2) and a daily surface brushing The coupon was removed from water after one week
6	#3 - Acid Start This coupon was acid started for one week, with a daily pH check (maintained at 4.5) and a daily surface brushing The coupon was removed from water after one week
7	#4 - Traditional Start This coupon was traditionally started for one week, with a daily pH check (maintained at 7.5) and a daily surface brushing The coupon was removed from water after one week
8	#5 - Traditional 30 This coupon was traditionally started for one week, with a daily pH check (maintained at 7.5) and a daily surface brushing The coupon then remained in pH 7.5 water for an additional three weeks for a 30-day cure
9	The Etched Sections The last three sections, which were identical to the traditional/30 section, were then etched – one lightly, one moderately, and one heavily What the lab found actually matches what we already surmised from experience, but the processes have now been scientifically documented
10	The Etched Sections Light Etch – pH 6.5 for a week… what will happen? Medium etch – pH 4.5 for a week… what will happen? Heavy etch – acid wash out of water with undiluted muriatic acid… what will happen?
11	#6 – Light Etch This coupon was traditionally started for one week, with a daily pH check (maintained at 7.5) and a daily surface brushing The coupon then remained in pH 7.5 water for an additional three weeks for a 30-day cure The pH was then lowered to 6.0 for one week
12	#7 – Moderate Etch This coupon was traditionally started for one week, with a daily pH check (maintained at 7.5) and a daily surface brushing The coupon then remained in pH 7.5 water for an additional three weeks for a 30-day cure The pH was then lowered to 4.5 for one week
13	#8 – Heavy Etch This coupon was traditionally started for one week, with a daily pH check (maintained at 7.5) and a daily surface brushing The coupon then remained in pH 7.5 water for an additional three weeks for a 30-day cure The coupon was then removed from water and heavily acid washed
14	Lab Results Coupled with the many other coupon and actual pool plaster analyses performed by this lab, a picture has emerged of the consequences of both the startup chemistry and the effects of acid attack We will cover the startup chemistry in a different presentation The following slides help show what is happening to plaster when it is put in water
15	Step 1 - Submersion This is a graphic representation (from top to bottom) of the water, plaster, gunite, and dirt
16	Step 1a - Submersion This is an SEM image of the “dry” coupon showing no effect yet at surface
17	Step 2 - Decalcification Once under water, the plaster releases calcium hydroxide, creating a calcium-depleted zone at surface
18	Step 2a - Decalcification This is the “traditional” coupon showing the calcium depletion at surface
19	Step 3 – Plaster Dust This calcium hydroxide reacts with bicarbonate in the water to form a calcium carbonate precipitate – “plaster dust”
20	Step 4 – Diffusion As the concentration of calcium in the depleted zone becomes lower than that of the underlying cement paste, calcium “migrates” into the depleted zone to “even out” the distribution
21	Step 4a – Diffusion This SEM shows a band of calcium diffusing into the depleted zone to even out the distribution
22	Step 5 – Carbonation As bicarbonate (part of the alkalinity) reacts with calcium hydroxide in the surface plaster it forms a protective carbonation layer (of calcium carbonate)
23	Step 6 – Decalcification and Diffusion The decalcification and diffusion processes continue until the carbonation layer is sufficiently formed to block those processes
24	Step 6a – Decalcification and Diffusion This SEM (of the “cured 30 days” coupon) shows the protective calcium carbonate layer
25	Step 6b – Decalcification and Diffusion This EDS shows the composition of the protective layer: almost pure calcium carbonate (CaCO₃)
26	Hallmarks of Aggressive Attack Eating away of the cement part of the surface Excess porosity in that eaten area Breakdown of the sand exposed at surface “the [etched] specimens all share characteristics of surface cement paste erosion and evidence of calcite aggregate dissolution” (Dr. Clark) Uniform effect across the surface
27	Light Etch The protective layer was compromised (i.e., the surface was eroded), aggregate is rounded, and additional calcium is migrating to surface
28	Moderate Etch The protective layer was compromised (i.e., the surface was eroded), aggregate is rounded, and the surface (to date) has been affected beyond the ability to form an additional quality protective layer
29	Heavy Etch The entire carbonation and decalcification zones have been eaten away, and even the aggregate is eaten into
30	Laboratory Results The carbonate layer acts to protect the underlying cement paste from solutions permeating the surface. In the traditional sample it is very incomplete In the case of the Cure 30 sample the protective layer is incomplete, with breaks in the layer occurring near or along aggregate at the surface. In the Lite etch it is compromised In the Medium etch it is very affected In the Heavy etch it is gone
31	Laboratory Results “Micro-structural features indicative of the swimming pool industry’s ‘aggressive water’ are observed in the Lite Etch, Medium Etch and Heavy Etched samples. While a region of porous, decalcified paste is present in two of these samples (not present in the Heavy Etch sample), the specimens all share characteristics of surface cement paste erosion and evidence of calcite aggregate dissolution.” (Dr. Clark)
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