What is plaster and gunite?
Plaster is the coating over the gunite pool shell that is made of crushed white marble dust. Gunite is the concrete shell of the pool with rebar enforcement. Standard depth of plaster should be no less than 3/8" thick, this requires two coats of plaster to be trowelled onto surface.
What is the purpose of plaster?
Plaster is needed to have the smooth touch on your pool surface. Plaster is at its smoothest when it is new. This is when the plaster has no erosion or calcuim build-up on the surface. Once erosion occurs the surface gets very rough and creates pits for algae to grow into the pool walls and floor (causing problems with repeated algae formation in short periods of time.)
How long should plaster last?
White marble plaster should maintain its smoothness and whiteness about 5-7 years before you should notice any type of erosion. Water chemistry should be properly maintained at all times to get a longer life out of your plaster. Other coatings will last longer but will cost a little more. Additives can be introduced into plaster to add life and durability as well.
What is a pop-up and what causes it?
A pop-up is a term to describe a round hole on the pool surface where the plaster did not bond to the existing surface and has pulled away. Normally this does not happen to the original plaster of the pool because it is directly applied to the rough gunite. This happens most commonly to replastered pools, when the surface is not properly prepped and made rough enough for new plaster to bond to. Replastered pools should have a rough (primer coat) applied to old plaster before the new layer is trowelled on.
Are there different types of plaster and pool coatings?
Yes. Although white marble plaster is the most common and the least expensive gunite coating, there are many new types of coatings available now. For years the only way to achieve a different look to plaster was to add blue, gray, black, or green dye to white marble. However, in the last 10 years, aggregate coatings have become very popular due to its durability and versatility in colors and shades. Diamond Brite Aggregate Coating is the most common of these aggregate coatings. This coating should last 2-3 times longer than white marble plaster because aggregate is much more durable than marble dust. You should expect to pay about 50% more for this coating.
Another type of coating is Fiberglass
Unfortunately, this is a great coating only for a few years (maybe 5 at the most). This very expensive coating has two major problems with it. One is the fact that if it is applied over the top of a white marble plastered pool, it tends to delaminate from the pool surface. It causes the white plaster to pull away from the gunite shell (large bubbles start to occur and eventually tear). Fiberglass coatings must be applied directly to the gunite to have a strong bond. Fiberglass installers should take off all existing marble plaster from the pool surface before it is applied to the pool (most will not do this). The other common problem is that if proper water chemistry is not maintained at all times, the resin that holds the fiberglass together begins to break down. This actually causes fiberglass shavings to come loose and suspend in the water and causes pits to surface for algae to grow into. Lastly, many types of additives have come out in the market (too many to list). All of them have good qualities and make white marble plaster more chemical resistant. Usually these additives are only a few hundred dollars extra and when added to manufacturers' specs can help to maintain a good looking pool for many more years. Most of the additives help to create a seal in the plaster so that the pool water chemistry cannot erode the plaster as quickly.
What causes stains in plaster?
Stains are caused by many factors. Leaves and tree debris have pigment that can stain plaster. High amounts of metals in your fill water causes stains. Old pool equipment made of brass, iron, copper, steel, etc. causes metals to get into the pool. Most new pool equipment is made of fiberglass or high tempered plastic to reduce metal breakdown. Fertilizers used to fertilize your yard have iron in them as well, which can be accidentally blown into the pool. Some large rust stains in plaster can be rebar or the tie wire of the rebar in the gunite shell bleeding through to the surface of the pool. The pool shell should be cut or chipped out to remove this piece of metal if possible.
How can I make my plaster last longer?
Proper water chemistry is the key to long life of plaster. Brushing and cleaning the pool surface is very important also. Pools not brushed or vacuumed for long periods of time will cause black algae to grow on the pool surface. This algae is very hard to get rid of once it has started because it has a very strong and thick coating the older it gets.
How do I know I need to replaster my pool?
When you can no longer keep control of the algae that has grown into the pits of the plaster. When you see the gray gunite shell show through thin plaster. When plaster has many pop-ups. When the pool surface is rough to walk on, snags bathing suits, or pool cleaner parts seem to be wearing down in a short time (tires, wear rings, hoses, etc.). When plaster has blue/green or orangish stains from high amounts of metals in water.