One choice for waterproofing your swimming pool is by using an external slab membrane, otherwise known as a sandwich membrane. This is a sheet or liquid membrane that goes between two layers of concrete. You could also use a direct bond waterproof membrane. These protect the underlying levelling mortars and concrete shells from water. Another option is to use chlorinated rubber paint. Once this is applied it is 100 percent waterproof. An advantage of chlorinated rubber paint as opposed to other types of waterproofing paint is that it can be applied in a thin layer. Water based waterproofing paints need to be applied very thickly in order to work properly. Cementitious waterproofing is the most preferred type of waterproofing for swimming pools. Cementitious waterproofing uses a cement based compound that has special additives and is mixed with water and liquid bonding agents in order to give a waterproof coating. The mix is applied in slurry form. Cementitious products are able to resist the constant pressure of the water.