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Pre-Slope needed for a new shower pan?

We're in the process of remodeling a small master bath. We removed the old fiberglass stand-up shower unit and are going to put in a new tiled one. Floor area of the shower is roughly 3' by 4.5'

The plumber put in a new drain but it current comes up flush with the subfloor. His idea was that you then put in a membrane and then create your mortar slope and tile over it.

I had read that you want to create a pre-slope first - then put in the membrane and then continue with mortar and tile on top of that.

How vital is the pre-slope? My understand is if water gets through the 2" of tile and mortar and hits the membrane - if it is sloped it'll help channel water down to the drain area...

Re: Pre-Slope needed for a new shower pan?

The sub-slope is a requirement in the plumbing code: "All lining materials shall be pitched 1/4" per foot to weep holes in the subdrain..." This pitch is usually created by a sloped bed of dry-pack sand mix placed over a layer of metal lath to keep it from fragmenting. Tile setters usually know more about this than plumbers.

The mortar base that is then placed on top of the liner is also sloped.

Also, be sure that, once the liner is installed properly, a flood test is done on the pan liner. This is done by plugging the drain tailpiece below the body of the shower pan drain, and filling with water to the level of the threshold. It should hold water for 24 hrs. If your plumber did not know about sub-slope, he may not know about the flood test.

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