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Shower pre-slope discussion

Posted by weekendwarrior_2009 (My Page) on Sun, Mar 22, 09 at 19:51

I just spent a day "discussing" the installation of a shower membrane with the guy I hired to retile my master bath. He wanted to install the shower membrane over the backboard. I won that is installed behind the backerboard now. Then I did more research (checking up on him) and asked about the pre-slope and he started with the "in umpty-ump years I've been doing this..I've never" speech. He already layed in the mortar for the shower floor on the membrane and I have that sinking feeling in my stomach. Is the pre-slope a big deal and what is the potential issue for installing the membrane onto the subfloor? He told me that the mortar bed has a slope that will take care of the water. Pardon my tone, but this has been a internet, doing by the book weekend guy vs. the old school handyman kind of week. Any advice? Thank...this is a great forum. I wish I found about two weeks ago.



RE: bathroom tile FAQ's

Posted by bill_vincent ( on Mon, Mar 23, 09 at 9:38

"in umpty-ump years I've been doing this..I've never"

If he started putting it over the backerboard instead of behind it, obviously this moron has no idea of what he's doing. That would've been my cue to fire him on the spot.

Is the pre-slope a big deal and what is the potential issue for installing the membrane onto the subfloor?

Yes, it is, although not many tile installers, plumbers, or GC's realise it. There are two potential issues. First, the given that lends credibility to these issues-- tile, grout, thinset, and mortar ARE NOT WATERPROOF. This is the reason the liner goes underneath all of them.

Now, the first issue is that being that the pan membrane sits flat on the floor, there will always be water sitting in the bottom of the mud base. It needs the help of gravity for ALL the water to reach the weepholes at the base of the drain. With the water sitting there, collecting all kinds of gunk and garbage, it's the perfect breeding ground for mold, mildew, bacteria, and fungus. Is that what you want to be standing on as you get clean?

Secondly, if he set the membrane flat, I'd be willing to bet he just set the cement board in, and dropped it right to the floor, being that it's much easier than holding up an inch or so, so that it's not sitting on the bottom, but so that the mud still covers it. Why THIS would be a problem is that with standing water in the pan, the cement board will act like a straw, and wick the water into it until the water reaches the top of the membrane, where it will spill out and over, causing what appears as a leak.

This NEEDS to be addressed.

Please do me a favor, and post this discussion over on the discussions side, so more people will see it and benefit from it.


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Posted by weekendwarrior_2009 (My Page) on Mon, Mar 23, 09 at 11:44

Thanks Bill for the quick response. Please disregard my e-mail. I will let you and the other members know how this works out. It appears that just putting the fiberglass pan back would be the easiest. FYI, the walls of the shower are tiled down to about 18 inches above the floor so I am looking for the least destructive way to correct this...with a new contractor. Thanks again.

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