Pool Plaster

Pool plaster, ideally, will appear white after it has dried. Usually, however, grayish areas will crop up in the plaster. This color variation is known as mottling and is a natural coloring effect that most plaster jobs eventually show. Though not necessarily attractive, mottling is not considered a defect. Don’t worry about trying to fix the problem; recently a lot of research has been done on the causes of and cure for mottling, but no one can agree on just what causes the effect or how to fix it.

Staining is something quite different from mottling. Stains on pool plaster are distinctly colored localized spots, usually caused by heavy metals precipitating out of the water. Most stains are caused by copper, cobalt or iron, all of which leave green, red, or blue stains, but they can also be caused by calcium which leaves white crystals. Manganese leaves pinkish red stains. If you notice staining of any color, use a sequestering agent to help the pool water retain the metals in solution. The stains themselves can be removed with an acid wash.

Crystalline deposits, which will leave areas of your pool that feel extremely rough, are caused by metallic salts precipitating out of the water. There are several solutions available for removing crystalline deposits, including acid solutions. Crystalline deposits can also be sanded off the pool plaster.

Etching, which you will notice as beige spotting on the pool plaster, is usually caused by water with a pH imbalance. If your pool water isn’t too acidic, then the problem may be with the original plaster mix or with the gunite under the plaster. If this is the cause, you will need to re-plaster your pool.

If your pool plaster appears to have small cracks, it is said to be checking or crazing. Crazing is caused by extreme fluctuations in temperature, usually during the initial plastering. The crazing is not too much of a worry as it is only a blemish on the surface of the pool plaster. The cracks pose no structural issues or potential for leaks. Acid washing will take care of checking. If the scratches are large or appear to run deeper than the surface, you can cut out the offending section of plaster and re-fill the hole with a plaster patch.

You will notice bond failure, or delamination, in areas where the pool plaster has actually come off the sides of the pool. This is usually seen with poorly done re-plaster jobs and is repaired with a patch. Be careful not to confuse delamination with plaster deterioration. You can tell the difference between the two problems because pool plaster does not usually fail to adhere to gunite, only old plaster underneath. If it doesn’t appear that there are actual holes in your pool plaster, but instead you notice gray spots in certain areas, that is the gunite showing through the plaster. You cannot use a patch to fix this problem; you will need to re-plaster the pool.

Many of these problems can be avoided by properly maintaining your pool plaster. The most important thing you do for your pool plaster is to maintain a neutral pH for your water. The pH level in your pool water should be between 7.4 and 7.8. Any more alkaline or acidic and you will find your pool plaster becoming etched and pitted. As well, maintain a level of calcium in your water that is between 200 and 400 parts per million.

While it is easy enough to maintain or repair your pool plaster with patches or acid washes, most pool professionals advise against re-plastering on your own. The major risk is with getting the plaster mix right. All the problems mentioned above can also be caused by improperly mixed plaster. If this is the cause, you will have to re-plaster. Have a professional mix and apply your pool plaster correctly the first time, and maintain it properly, and it should last you a long time.