Chemical balance: Though there are several properties of unbalanced water that can be hazardous to plaster, calcium hardness imbalance is probably the most damaging. When the calcium hardness goes too low, the water will attempt to leach the calcium from the plaster, leaving the plaster rough and pitted. When the calcium level goes too high, the water will deposit excess calcium on the plaster, leaving rough nodules that will require sandblasting or acid washing to remove. Note: the ideal range for calcium hardness is between 200–400ppm.
Metals, mainly iron and copper, in your pool water can cause extensive staining of the plaster. You should have the source water (especially well water) tested for metals before adding any water to your pool. If the water tests show any metal content, you will need to use a sequestering agent as part of a weekly maintenance schedule. Note: the ideal level for metals is 0.0 –0.1ppm.
It is also important to keep the pH and alkalinity stable. If the pH and alkalinity drop too low, the pool water is acidic and will etch the plaster if left low over time. If the pH and alkalinity go too high, the water is basic and will form “scale” on your plaster over time. Note: the ideal range for pH is 7.2 –7.6ppm, and the range for alkalinity is 80–120ppm.
Algae prevention: The key to algae prevention is a maintenance routine that includes monitoring the chlorine level, shocking the pool, and adding an algae preventative on a weekly basis. If you notice a patch of algae on your plaster, it is extremely important to kill it as quickly as possible for two reasons: algae can and will get out on control, and if left unattended it will embed itself in your plaster. To kill algae, you must use an unstabilized chlorine shock and an extra-strength algaecide. Algae problems will leave the plaster dingy after a period of time.
Stain prevention: Staining can occur from sources other than those mentioned above, such as: leaves left on the plaster, or the introduction of foreign objects (equipment with metal parts, coins, etc.) to the pool water. The key to preventing these kinds of stains is communication between the pool caretaker and anybody that uses the pool. Be sure to remove leaves and other debris as often as possible, and let all bathers know to keep equipment with metal parts out of the pool. Note: the only ways to remove stains are through re-plaster and acid -wash. Acid washing shortens the life of the plaster, and should be considered only if there are no other alternatives.
Hydration: It is vital to the life of the plaster to keep it fully covered with water at all times. If plaster is left dry over time, it will crack. If the cracks are not sealed properly, the cracked areas can chip off.
Circulation: The circulation of the water fortifies the plaster and accelerates the curing process. During the first month of the plaster, the water should be circulated continuously.
Proper winterization: Due to the hard winters in this region, it is recommended that the pool be professionally closed, to prevent pipe, equipment, and tile damage. During the winter, the water level must be maintained 3” below the waterline tile for plaster pools, and at least below the skimmers for vinyl liner pools.