By Melanie Rekola
Pool surface finishing is a sought after expertise as no matter how well a concrete pool is built, there comes a time when restoration may be needed. Pool plastering (otherwise known as marbelite) is a highly specialized skillset. Unlike other areas of masonry surfacing, marbelite belongs to its own distinct category as its finishes are unique in that they are constantly submerged in water. The following is a guide for pool builders and renovators on the various marbelite finish options available as well as some installation tips, tricks, and cautions.
What is marbelite?
Marbelite pool plaster, which comprises a mixture of fortified white cement, white marble dust, and other additives, has been used by industry professionals for more than 50 years as an interior finishing product designed for resurfacing gunite or shotcrete pools and spas.
This cement-based concrete mixture can be left a classic white, or customized by adding colour to the mix and/or a specialty finish, e.g. coloured quartz, pebble, or glass bead. When applied properly, pool plaster can transform ordinary and old unsightly concrete into a beautiful and practical surface that is resistant to chemicals, algae, and staining.
Pool plaster and water interaction
It is important to note, every pool finish is exposed to fluctuating water chemistry conditions. It is this constant exposure to pool and spa water (which is treated with a variety of chemicals) that creates a dynamic environment where mineral content of the vessel’s surface and water are constantly interacting. This interrelation between water and surface is unavoidable. In many cases, it will cause the appearance of the pool or spa surface to change—either slowly over time, or more rapidly in some rare occasions. In many cases, this phenomenon is purely cosmetic, while in other, more extreme, situations some surfaces will start to deteriorate.
Therefore, the importance of balanced water chemistry cannot be overstated as it is essential to the lifespan of every marbelite application. It is especially important to understand should heavy amounts of metals (i.e. copper [Cu] and iron [Fe]) precipitate in the pool/spa water it may result in unsightly stains around a new pool plaster finish. The correct water chemistry table to abide by is shown in Figure 1 below.
|pH||7.4 to 7.6|
|Cyanuric acid (stabilizer)||Below 50 parts per million (ppm)|
|Alkalinity||80 to 120 ppm|
|Sequestering agent||10 to 20 ppm|
|Free available chlorine (FAC)||1 to 3 ppm|
|Combined chlorine||0 ppm|
|Total available chlorine (TAC)||Equal to FAC (represents 0 ppm combined)|
|Calcium hardness||200 to 400 ppm (below 250 ppm for exposed aggregate)|
|Total dissolved solids (TDS)||Below 1200 ppm or no more than 800 ppm above fill water|