BobVila.com

You are going to need a waterproofing membrane under the floor of the shower and extending up the walls about 8". Otherwise as the water migrates through the grout and into the cement under the tiles it will go to places it should not go. The new pan will be a self contained unit that keeps the water inside the unit and directs it to the drain via weep holes in the base of the clamping flange and employs a preslope so that water does not stand and become musty in the cement bed. I know I am throwing some lingo at you that you may not understand. Rather than bore you with the details here go to www.ontariotile.com and look at their section on building a shower pan. It will explain in greater detail what I have talked about.

Thanks!