Pool plaster mix refers to the finishing coat given to a concrete pool. Its purpose is to make the pool surface smooth and to provide a watertight seal. It also gives an aesthetic appeal. Approximately 0.25 to 0.5 inches thick plaster layer is used. White is the most common color, but other colors can be obtained by the application of pigmented aggregates. Proper maintenance is required to give a life of 20 years.
Ingredients
The pool plaster mix elements include, White Portland Cement along with aggregates such as limestone, quartz sand, marble dust, etc., in the ratio 1:2. Liquid acrylic concrete fortifier is needed to mix these constituents. It provides durability to the Pool Plaster Mix due to its constant immersion in water.
Maintenance of the mix
Pool plaster mix offers a higher expected life. In practical terms, it boils down to the maintenance and the water chemistry. Acidic conditions (low pH) etch the plaster, causing a pitted, rough surface leading to faster degradation. Alkaline conditions (high pH) cause scaling and later discoloring of the plaster. Copper, Iron or other minerals cause stains, while acid washing is a result of algal issues deteriorating the pool plaster mix.
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Guidelines to produce an effective mix
As the plaster mix needs proper maintenance, a few guidelines are recommended. Using aggregates in the ratio of 1.5-1.75 to 1 part of cement is recommended. Using excess cement causes cracking, while excess aggregates reduce the durability of the pool plaster mix. A thick mix is often preferred. Both the Portland Cement Association (PCA) as well as the American Concrete Institute (ACI) recommends a maximum water-cement ratio of 0.48. In fact, they advise even lower ratios to withstand exposure to mild acids, increase density, reducing porosity, shrinkage and permeability.
Mixing more than 90 minutes must be avoided. The swimming pool plaster mix is best when it is used in the preparation. The mix should contain a minimum calcium chloride set-accelerant and not more than 2% white cement. Excess calcium chloride causes shrinkage and gray mottling discoloration.
Adding water to plaster surfaces should be avoided while troweling as it increases shrinkage, discoloration and porosity. Using a little water to lubricate the trowel does not have any profound effects on the quality of the pool plaster mix. Extreme weather conditions cause durability and quality issues. It is normal to finish plastering as soon as possible. However, plastering requires a minimum of 4 hours. Any plastering work done in less than this time is bound to have durability problems in the long run. The Pool Plaster Mix needs to dry for some time, before it is filled with water. The usual time is 6 hours, but the existing weather conditions play a significant role. An important point to be understood is that the bottom is the last portion to be plastered and hence, checking only the walls will not give a proper opinion. The last guideline of all is to keep the water pH level balanced. Excess acidic or alkaline conditions weaken the pool plaster mix.