How to choose a good pool plaster finish



Why are some pool plaster finishes more durable than others? A good plaster finish is one that is durable and also looks good. To be able to understand why some pool finishes are more durable than others, you must have some understanding of pool finish materials.

This post will primarily focus on the aggregate portion of the plaster mixes. The most common aggregates used in pool finishes are marble dust, quartz, and pebble.  It is the aggregate that is the variable and the major factor in every finish that helps determine if it is more durable or not.  Cement is more or less Calcium.

The Mohs Scale is used to measure the relative hardness of a mineral by its resistance to scratching. From softest to hardest, the ten minerals of the Mohs scale are talc (measuring 1 on the scale), gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, and diamond (measuring 10 on the scale).  

Consider the difference between numbers in the Mohs Scale similar to the differences between and 2.0 and 6.0 earthquakes. The difference between the relative numbers on the Mohs scale are similar in distances apart as the earthquake numbers are different in relation to the damage that results from a 2.0 compared to a 6.0 earthquake.

Marble Dust registers at a number 3 on the Mohs Scale.  It is a very soft material. When a simple acid test (submerged in acid) is performed on marble dust, it completely oxidizes with nothing left.  When this same test is performed on both quartz and pebble, nothing happens. Quartz and pebble register at a number 7.0 on the Mohs Scale. The quartz and pebble are unaffected by the acid test.

The acid test is done to simulate aggressive pool water chemistry. If you have white plaster, it has marble dust in it as the aggregate. If your pool water is out of balance at any time the plaster will be damaged. White plaster is too weak to last for a long time even if the water chemistry is perfectly balanced.

Quartz and pebble finishes installed by National Plasterers Council members will outlast white plaster. White plaster should not be used in swimming pools.