Plaster/marcite is a combination of cement, sand, and calcium carbonate (plaster dust). When applied it is troweled until the “cream” is brought to the surface. In that cream is calcium carbonate and cement. The cream hardens and becomes a protective layer. It is approximately the thickness of two to three sheets of paper. This is why an acid bath is damaging to plaster/marcite, because the protective layer is so thin. In addition, you have two dissimilar surfaces, the protective layer and the sandy cement material underneath which will cause separation or popping if the pool is left drained.
Plaster is typically the preferred finish for indoor pools. It has a longer life-cycle than paint but doesn’t have the longevity or aesthetic appeal of tile.
For pneumatically applied concrete pools, plaster is much easier for the contractor to finish than paint. If the contractor intends on shooting the pool shell, plaster and paint may be very close in cost because the wet concrete will need to be troweled to a smooth finish after it comes out of the gun.
When plaster spalls, old plaster sections, which have not spalled, are frequently weak. As a result, re-plastering creates a scenario of putting good plaster on top of bad plaster. For this reason, plaster contractors seldom guarantee the re-plastering of a pool surface. The only sure way to re-plaster a pool is to sand-blast or water-blast the walls and floor down to bare concrete, which is an expensive and time consuming process.
In outdoor pools the plaster coat may separate and create a hollow space between the plaster coat and the pneumatically applied concrete pool wall. This develop usually occurs after 10 – 15 years and is likely accelerated by freeze/thaw cycles.
Re-plastering after plaster fails is difficult with regard to a quality control. Because new plaster is being applied to older, weaker plaster, most experienced contractors will not warranty their work because re-plaster projects frequently fail in a short period.
Pool plaster delaminates or spalls due to improper installation not poor water chemistry.
Plaster is made up of cement, sand, and water.
Pool plaster is commonly troweled in 3 to 5 separate passes – the early passes to place the material and the later passes to create a smooth final finish.
After plaster is troweled, excess water will bleed to the surface. Bleed water then evaporates from the surface.
The Division 13 Cementitious Finish Specification includes a 3 year warranty on all cementitious finishes, including plaster.
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