A shallow swimming pool is ideal for young children and for saving money. Less depth means less water, so you can save on the costly chemicals that are needed to keep the pool sparkling clean. A decrease of up to 12 inches can be achieved by adding concrete to the bottom of a pool that's approximately 12-by-24-foot. This project can be done when replastering the pool, which is when the old plaster is removed completely and new plaster is applied to the entire surface.
Connect the 100-foot hose to the submersible sump pump, near its motor. This type of pump can be rented from hardware stores. Place the free end of the hose into the gutter in front of your home, so it drains into the sewer.
Lower the submersible sump pump into the pool's deep end while holding onto its electrical plug. Plug its electrical plug into a 100-foot heavy duty extension cord. Plug the other end of the extension cord into an outdoor electrical outlet. This automatically turns the pump on. It may take up to 12 hours to drain a 12-by-24-foot pool, depending on its depth.
Drag the chisel part of 16-ounce hammer across all the sides of the pool, and tap the bottom of the pool with it to test for hollow spots. Listen for changes in the tone, which are called hollow spots. Use a 6-foot ladder, if necessary. Hollow spots are areas where the plaster is worn. Mark these spots with red spray paint.
Wear safety goggles and gloves. Point the 1 1/2-inch flat chisel at a 45-degree angle 1/2-inch away from a found hollow spot. Strike the end of the chisel with a 16-ounce rubber mallet to chip away the hollow spot. Repeat at the opposite side of the hollow spot. Chip around each hollow spot to remove completely.
Grind below the interior pool tiles, about 1 inch deep and 1 inch wide, using an angle grinder. Hold the blade at a 90-degree, just under the bottom of the tiles, to cut a 1 inch deep cut into the sides of the pool. Then angle the blade at a 25-degree angle below the first cut to remove about 1 inch of pool plaster. This prepares the areas for the new concrete. Repeat the same procedure for grinding around fixtures, such as the lights.
Wear a N-100 respirator, gloves, sandblasting hood, long-sleeved shirt and goggles to prepare for sandblasting. Position the nozzle of the sandblaster all the way open. Turn on the main air valve. Open the sand air valve to the 6 o'clock position. Close the other valves.
Point the nozzle at the deep end pool wall first. Open the sand valve slowly. Blast the wall in circular motions to remove the flaky old surface. Sandblast the side walls next. Step over to the shallow end. Sandblast the bottom at the deep end and then the middle bottom. Turn around, and sandblast the very shallow end and steps. Turn off the sandblasting equipment, and remove the respirator and hood.
Brush off any black algae with a wire brush. Use circular motions at any spot where black algae is found. If this step is not taken, black algae can grow back after the replastering.
Mix together a 80-pound bag of pool concrete with enough water in a trough to create a thick porridge-like consistency for a bond coat. Combine one part concrete to one part water, or follow the product's instructions if it varies. Approximately one 80-pound bag is enough for the thin bond coat. Dip a 9-by-3/4-inch poly paint roller into the concrete. Roll a thin coat of concrete over the entire surface of the pool. Allow it to dry overnight.
Mix together two 80-pound bags of pool concrete with water for the sides of the pool. Rent an electric drum cement mixer with a 200-pound capacity, and mix the concrete inside the pool. Work with two bags of pool concrete at a time. Add enough water to form a porridge-like consistency.
Scoop up approximately 1 cup of concrete with the side of a stainless steel pool trowel. Smooth it onto the side of the pool in swirling motions, starting at the deep end. Apply the concrete to the sides of the pool in 4-foot square sections. Pick up more concrete with the trowel, and swirl it onto the surface. Build up the thickness to 3/8 inch, and smooth the concrete as evenly as possible.
Mix together more concrete, two bags at a time, inside the pool to make it shallower. Pour the concrete into the bottom of the pool, starting at the deep end, directly from the mixer. Slowly build up the depth by pouring in concrete and swirling it smooth with a trowel. Allow the concrete to cure according to the product's instructions or for 2 hours.
Mix together two 80-pound bags of pool plaster in a ratio of 1-to-1 with water, in a trough, according to the product's instructions. Scoop it up with a trowel, and use a swirling motion to smooth it on. Work the deep end sides first, and continue toward the shallow end in 4-foot square areas while the concrete is slightly wet, for better bonding.
Mix together the two remaining 80-pound bags of pool plaster. Build up the plaster's thickness to 1/4 inch. Allow it to dry completely overnight. Replace the lights and other fixtures.