Why does the water from my shower stain the bathroom floor?

QUESTION

Why does the water from my shower stain the bathroom floor? We installed a handicap type dam-less shower pan and bathroom floor with limestone tile. We ran the waterproofing sloped into the shower and to the drain with a typical mortar bed float application. The bathroom floor has waterproof membrane similar to shower pan. The stone tile at the edge of the shower slopes to the drain but the bathroom floor is level. The bathroom floor has an electric heating pad in it. The moisture from the shower wicks back onto the bathroom floor and stains it. The heat pad accentuates the staining issue. Do you have any suggestions how we could correct this or put me in touch with someone who could help?

ANSWER

ANSWER - I just wrote an article for the Construction Specifier that will be published in May 2013 that talks about this type of problem and potential causes.
Key things to look at are:


1. pre-slope under waterproof membrane is to be 1/4" per foot slope and flat within that plane.

2. Weep holes at drain have to be protected with pea gravel or weep hole protector to keep weep holes open to allow water that reaches membrane to evacuate.

3. shower floor to bathroom floor transition should have a movement joint that goes down to membrane level.  Edge of shower pan mortar bed should be            flashed/treated with waterproofing liquid.  Transition joint is to be filled with polyethylene back-up strips and then caulked with an ASTM C920 traffic grade sealant.  This also acts as a water-stop so water doesn't migrate to bathroom floor.


For enough water to migrate into bathroom floor from shower I would suspect that the pre-slope under membrane wasn't adequate and/or drain weep holes are plugged. good luck.

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