Basically there are two main types of plasters - the cement based plaster and the gypsum based one. When the slaked lime stops giving off heat, the mix is ready to be mixed with the putty. And this lime putty is the last coat of plaster. It gives the wall a hard and shiny finish coat. For outdoor work the cement based plaster is used. For indoors the gypsum based plasters are used. It is used outside it could be attacked by the damp and the wall may crumble. Once the pool is completely full up to the tile you will begin the process of brushing the pool plaster.