Pool plaster patch11/18/2023 ![]() It has been documented by both ACI and PCA that doing so (that is, “skewing the surface water-to-cement ratio”) increases porosity, shrinkage, streaking, spotting and variable discoloration. Water should not be added to plaster surfaces during troweling because of the strong risk potential. In fact, it is recommended that if the plaster has been mixed for more than 90 minutes, the batch should be discarded. Helpfully, alternatives to calcium chloride that lack this downside potential are available.Ī plaster mix should be mixed thoroughly, but not for too long. (Colored plaster, of course, should not contain any calcium chloride.) It has been documented by PCA and cement researchers that using more than this amount increases the chances of gray discoloration, mottling and cement shrinkage. Plaster should contain as little calcium chloride set-accelerant as possible - and never more than two percent of the amount of white cement. Lower water-to-cement ratios also increase density and reduce permeability, porosity, shrinkage (craze cracking) and movement of water within the cement product, while higher water-to-cement ratios can result in a finished product that does not offer adequate protection or long-term durability against the natural effects of water and the environment. ![]() 50) yield better quality cement that can resist occasional exposure to mild acids. ![]() The American Concrete Institute (ACI) and the Portland Cement Association (PCA) have established that lower water-to-cement ratios (that is, less than. Further, the cement and aggregate (and admixtures, for that matter) should be selected with care: All need to be of good quality and consistency and of an appropriate grade for use in pool plaster.Ī water-to-cement ratio of. Plaster that is too rich tends to shrink and crack, while plaster that is too lean is unworkable and isn‘t durable. This ratio results in a higher-quality pool plaster finish than either richer (more cement) or leaner (more sand) mixes. The best cement-to-aggregate ratio is about 1 part cement to 1.5 to 1.75 parts aggregate (marble sand) - with quartz finishes being a little richer in cement. To see the revised version, please click here. Kim Skinner has extensively updated this article. This recognition has in turn led to development of a list of ten basic recommendations that reliably result in the creation of durable plaster. In the process, we‘ve learned something unsurprising - that known principles of concrete/cement science actually apply to pool plaster. All of that has been dedicated to reaching a better understanding of plaster‘s performance, including the causes and mechanisms of problems ranging from etching, scaling and nodule formation to delaminations, spotting, staining and general surface deteriorations.
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