What type of gaps can thinset cover?


Old 09-23-16, 07:41 AM
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What type of gaps can thinset cover?

I'm building a powder room in our basement - three walls are studded and one is the cinderblock exterior wall. The whole room, floor to ceiling will be tiled with subway tiles and black 7/8" hex tiles.

There's no shower so I'm just going to tile directly to the drywall on the stud walls and ceiling (Any advice on ceiling - should I use mastic instead of thinset so it sticks better?)

What I'm really asking about is that cinderblock wall though. Its been painted several times through its 100 years and in a couple areas, the paint has flecked off and the concrete has eroded and crystalized a bit. These spots are no deeper than a half inch deep by maybe an inch tall, three inches wide. The plan is to scrub the hell out of the wall with a reciprocating wire brush (and a rotary brush), then clean the hell out of it, then simply apply the thinset directly to the concrete and tiles directly to that. I'm just slightly worried about those gaps. Do I need to patch them first or will just a couple (3-4) of these be no big deal. I should also note, none of the gaps is anywhere near as big as a whole tile. So there will just be 3 or 4 spots where the adhesive is 3/4" deep to fill a little valley. Will that be okay or will I be watching tiles fall off my walls in a couple years.
Also - do I need to prep the wall in anyway besides what I've described?

Yes, its my first tiling job. I'd love some advice on what thinset to buy too - the whole room, four walls ceiling and floor are a total of only 140 or so sq feet.
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Old 09-23-16, 08:03 AM
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Welcome to the forums.

My main concern at the moment is how much moisture you have coming through that outside wall.
Old 09-23-16, 08:59 AM
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The paint, especially the flaking paint and efflorescence causes me concern. Paint on the wall is bad enough but that it's coming off with signs of water is a problem. The paint would need to be removed to apply tile but fist the water issue must be addressed.

Most old basement walls were not water or damp proofed on the outside. So, even though you don't have liquid water pouring through you can have considerable water vapor passing through the wall. That is probably what's caused the paint to flake off and the fuzzy deposits to appear. Just brace yourself that this may not be quick, easy or cheap to remedy. There are no magic products you can just paint on the wall to stop the water.

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