Welcome Seanie, Hi Kevin,
It's not surprising to us that you've seen many shower pans built wrong without the pre-slope. Happens all the time since most plumbers aren't forced to build em right and there is no enforcement of plumbing codes in many jurisdictions.
Think about it. Where will the water that gets through the tile work go once it's trapped by the membrane? Swamp water anyone?
Jaz
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Tile 4 You..Troy,Michigan U.S.A.
www.tile4you.com KERDI Shower Specialist-DITRA Installs-Containers of TRAVERTINE direct, ship anywhere. SAVE 40-70%
I've NEVER made a mistake, I thought I did once...but I was wrong!