The busiest time of year for the industry, and it’s amazing how many calls we get from consumers and industry professionals alike with questions about swimming pool surface application and materials. One question we get on a continual basis is, “What exactly is swimming pool plaster?” Here’s a textbook answer to that question:

The pool cementitious surface coating consists of a mixture of hydraulic cement (typically white), white sands (typically limestone, quartz/silica or dolomite), and/or other aggregate, special additives (which aid in the placement and finishing of the cementitious surface), and water. The water reacts with the cement chemically to form a hard, rock-like material that, together with the sand and/or aggregate, creates a very strong coating. Supplemental (retemper) water often is added during mixing, giving the plasterer the ability to pump, place, spread and properly finish the cementitious coating. Cementitious surface coatings serve the useful purpose of lining the interior of the substrate structure or “shell” of a pool. Plasterers work the material with trowels to create a finish that is smooth and watertight. Cementitious surface coatings actually are semipermeable membranes and, as such, some amount of moisture slowly permeates these coatings.

As with many hand-troweled finish products, certain characteristic variations are to be expected as being inherent to the finish. Some fluctuation in the coloration, levelness or texture of the surface coating’s finish is to be expected, and is considered acceptable as a normal occurrence in all hand-troweled cementitious surface coatings. The benefits of the hard-trowel finish include increased density and smoothness of the surface, which, in turn, increases durability. The benefits of the colored aggregate finish, the exposed aggregate finish, or the polished finish, include aesthetic appeal and concealing of minor surface fluctuations.

Most cementitious surface coating complaints involve the following factors:
* Improper maintenance of the pool water and/or the coating surface.
* Workmanship or plastering application defects and/or failures.
* Material defects and/or failures.
* Normal or inherent fluctuations in raw materials, the plaster application, or the hydration and curing processes that are mistakenly considered to be flaws or failures.
* Some combination of the above.

Most issues with coatings can be remedied through modifying water chemistry or by treating the surface material. The NPC is proud of its 25 years providing sound technical practices that, if followed, add to the longevity and durability of a swimming pool’s surface.