Concrete subfloor is getting wet with rain, can I lay tile? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-13-2010, 08:16 PM
We have a home in Galveston, TX it was flooded in IKE and we found a couple weeks ago that underneath the existing floor tile was mold, so we pulled it up, most of it was not adhered to the concrete slab - the thinset was very well covering the tiles themselves but very little thinset was still on the slab.

The prior floor appears to have been vinyl tiles as there is the old black adhesive was on the floor. So we used muratic acid to etch the concrete and we were preparing to use modified thinset and new porcelain tile.

That's the background.... it rained last week and inside the dried in house, no leaks from the walls, ceilings or windows - there are now wet spots on the concrete floor - some from exterior walls and some from interior walls. Not huge spots but enough to make us worried. There are no visible surface cracks in the slab so not sure how the water is coming up from the bottom

Galveston is so close to sea level could this be causing it? And if it is, will we end up with the same issue again, tiles not sticking to the concrete in those wet areas?

The porcilan is expensive I didn't want to spend the money on that if we are going to have issues in the future.

I thought about using that liquid that bonds old and new concrete together.
any thoughts?

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Tool Guy - Kg
02-13-2010, 09:51 PM
Hi Beth,

What color was the "mold"? Do you have any photos? :)

Houston Remodeler
02-13-2010, 10:42 PM
We have tiled a number of slabs in Galveston, behind the seawall and along Lake Madeline. Never any issues with water penetrating from below. If your tiles are well adhered to the slab, flooding will not affect them. We had a house survive Ike with 17" of water. Tossed the fish outside, shop-vac'd the mud and water, the tiles are great. To dry your slab, use large industrial fans. Once the surface is dry, tile away. You will need an excellent thinset. Not the $5 a bag stuff from Home depot. You'll have to go off the island to get it. Or special order some thinset from HD, if you have good luck with that sort of thing with them.

02-14-2010, 09:18 AM
a lot of things can cause moisture in the slab, and you need to do a little more homework. The easiest thing to check is just your landscaping. Does the water run away from your house when it rains?

I don't recall the details, but there is also a test to run that basically entails taping about a foot square section of plastic over the floor and leave it for a few days. You are looking for condensation to collect. Tape it securely all around. (ok, so maybe those are the details :D )

Ditto on the thinset. You may also have to tend towards a dry-set type like Kerabond, or very slightly modified like Versabond.