When Doug and Que were members of the NPC Research Committee, there was committee discussion about the fatal flaws in the Dow Whitney study. Not only was the study poorly written and heavily plagiarized, it also focused primarily on pH, while many of the plasterer members of the committee were more focused on alkalinity as a causitive factor to plaster problems.

At Que's suggestion, a joint experiment was devised, wherein NPC members would form plaster sample coupons, and NAGC members would maintain those coupons at various alkalinity levels. The coupons could then be analyzed to learn more about the effects of various alkalinity levels on various types of plaster surfaces.

At the NPC Annual Conference in San Diego in 1999, two sets of sixteen coupons were formed, each about one foot in diameter and about one-half to three fourths of an inch thick. Each of the sixteen types was composed of a different cement and aggregate make-up. The water content and calcium chloride content were supposed to be the same in all sixteen coupons.

Each of the sixteen hardened coupons in each set was then cut up into quarters.
In two different locations, 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 adjusted to 40, 80, 120, and 160 respectively.

One quarter of each coupon was placed into each of the tubs - so each full coupon was now being exposed to water of the same pH but a different alkalinity. This water submersion and chemical maintenance and their respective chemistries lasted for 8 months. After 8 months, the quartered coupons were removed from the water barrels, reassembled, and inspected.

Among other things,a strange thing was noted about Set 2 Number 10. This coupon 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 the molded sides of the coupons were also subjected to the same water conditions as the troweled side!

We have previously mentioned that all but one of the onBalance plaster spotting case histories on our website were on actual pool plaster from spotted pools. This experimental coupon is the one exception - 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 substantially more that the 2% high end limit for calcium chloride.
- The coupon spotted at alkalinity levels of 40, 80, 120, and 160. 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.
- RJ Lee found the plaster spotting to be consistent to spotting in actual pool samples.