Things You'll Need
Hard-bristle scrub brush
Diamond Brite is a brand of plaster that some pool owners use to cover their gunite pools. Over time however, Diamond Brite plaster will become stained from the chemicals used in your pool. These stains can be removed by acid-washing your pool after the water is drained from it. Plaster more than 10 years old may need to be resurfaced. Acid-washing plaster near the end of its useful life can rub away and expose the gunite beneath.
Drain the swimming pool with your in-ground pool's drainage system. Remove any metal from the pool that can become damaged from the acid, such as ladders, railings, fittings and the drain cover. Stuff any fittings that lead to copper plumbing with rags soaked in baking soda, which will neutralize the acid.
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Put on your goggles, boots, gloves and respirator. Fill your pump sprayer with a 10 to 1 ratio of water to muriatic acid.
Spray the solution in small sections to the pool wall. Allow the solution to briefly soak into the plaster and then take the scrub brush and clean the walls. The stains will easily come off. Rinse each section of the pool with your garden hose when finished.
Rinse the entire pool again when you finish all sections of the pool. The acid solution and water will puddle up near the drain of your pool. Do not open the drain until the acid is neutralized. As a general guide, broadcast two lbs. of baking soda over the puddle for every gallon of muriatic acid used. Allow the acid-wash puddle to drain and reassemble the pool and its fittings.
Always handle muriatic acid with care, as it is highly corrosive. The gloves, boots, goggles and respirator must be worn to protect your skin, eyes and lungs from the acid and its odors.