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Plaster debate continues.

The recent letter by the Cal Poly professors (Jan. 17 issue, page 10) illustrates why there is confusion in our industry about the plaster spotting issue.

The central point is this: Aggressive water etches plaster uniformly, but spotted plaster is not etched. Instead, pool plasterers can cause "soft spots" (formerly and improperly called "spot etching") with improper plastering practices, leaving these areas very porous and susceptible to even balanced water.

Once this is understood, it becomes apparent that the Cal Poly professors have not been provided with all of the background information by their employers, the National Plasterers Council. Like the NPC, they use the two terms (etching deterioration and spot etching) interchangeably, yet fail to document that they ever studied or produced "spot etching" or, more accurately, soft spots. Until they do, it can and should be assumed that they are studying simple etching. And our industry already knows the cause of etching (aggressive water) and also the solution and cure: Balance the water!

Did Cal Poly get copies of the professional research lab studies that corroborated our work and if so, why were the points made in those reports not addressed? Why did the Cal Poly study make conclusions about the effects of water chemistry when the university failed to maintain the water chemistry within the stated target ranges?

Our position on soft spots has been proven by two of the best cement labs in the country, including the Portland Cement Association's own subsidiary lab, and their results are consistent with established science documented by the ACI. On the other hand, with regard to calcium chloride and water supplementation, Cal Poly's conclusions contradict current literature of the ACI and PCA.

We hope that they will do better in subsequent phases of their research.

Que Hales, Doug Latta, Kim Skinner


Tucson, Ariz.

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Title Annotation:Letters
Author:Hales, Que; Latta, Doug; Skinner, Kim
Publication:Pool & Spa News
Article Type:Letter to the Editor
Date:Feb 28, 2005
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