Swimming pools that are made of gunite, a type of cement, are prone to cracks even after a few years of being built. Gunite is the material that is underneath the pool's plaster. You need to perform periodic maintainance on the gunite in order to keep your pool in good shape. Cracks, hollow spots and chips are common with gunite pools, but you can easily repair these problems with tools rented from a hardware store.
Drain the pool completely and let it dry for three days.
Wear safety goggles and gloves. Cut out the crack using a saw with a grinder, which you can rent at a hardware supply store. Enlarge the crack an inch on all sides to be sure to get out all the cracked gunite.
Brush away the dust with a small brush or vacuum.
Squeeze a line of caulk on the inside of the crack, all along the inside. Fill up the crack almost up to the top, but leave about 1/4 inch of room at the top to pour in the plaster.
Let the caulk dry for 24 hours.
Mix together a batch of "pool patch," which is cement with sand and a bonding agent. Stir it together until it is the consistency of peanut butter.
Dampen the surface of the crack with a sponge. Fill in the crack with the pool patch mix using a putty knife. Pack it down as tightly as possible and smooth the surface so that it is even with the rest of the pool wall.
Fill the pool immediately with water.