I am having a shower installed in my basement. The shower is approx. 2.5' by 4'. I am having an cultured marble type of material installed in the shower. It is 3/4" thick on the base and 3/8" thick on the walls. The installer indicated that he wants to wait until I have the water-resistent drywall or cement board installed before he proceeds. He would then come in and install a vinyl liner directly on the cement floor (no pre-slope) and the vinyl would not be behind the wall board. He then puts down a bed of mortar and install the preformed presloped cultured marble base and glues the walls to the wallboard. Is this going to last or am I just asking for trouble?
This is a common installation for a shower floor that is not utilizing a shower ‘pan’, which has a built-in dam on all four sides. But, the floor should be thicker than ¾”. It sounds like they may be making a simple ¾” slab of marble and warping it so the water flows towards the drain. When installing a warped piece of marble for a shower floor, it leaves it vulnerable to cracking if the mortar doesn’t fill in all the voids. There is a shower base mold made for this and is commonly referred to as a Universal Shower Pan Mold. The proper slope is built in to the mold and the bottom lays flat on the floor. No warping and no chance of cracking. Another option is to use a shower ‘pan’ which would not require the vinyl but these only come in standard fixed sizes. If the area you’re installing a shower is not an exact size of a standard size shower ‘pan’, you can always have them install a bench if there is enough room or a shelf if it’s only a little bigger than a standard size shower pan size. Summing up; don’t install a ‘warped’ piece of marble for a shower floor. It’s a disaster (crack) waiting to happen. Find someone who can produce a shower pan from a mold made for this purpose.