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We recently installed slate tile in our renovated bathroom. We have sealed it with a penetrating water-based sealant. Water still seams to soak in to the tile and little water spots on the tile are appearing (and staying) after two coats of sealer. My wife is not pleased. I am worried about the slate we will be putting in the shower walls. Will it just soak through? Any ideas?

p.s. If my wife is not pleased, I am not supposed to be pleased ;)

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I'm not sure about a sealant, but when you're doing the shower be sure to install a waterproof membrane or backer board. Natural stone and grout is porous, and you don't want to rely on a non-permanent chemical coating to keep water out of your walls. –  Shimon Rura Apr 8 '11 at 3:12
    
Shimon: Agreed, the shower has been built with all the usual stuff, yet if the slate is constantly soaked it can't be a good thing. –  Matt Dowell Apr 8 '11 at 13:05
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What sealer did you use (band or at least type/ingredient)? –  auujay Oct 5 '11 at 20:44

1 Answer 1

up vote 5 down vote accepted

You likely need more coats of sealer. Depending on the porousness of the tile and the quality of the sealer you may just need more to get the job done.

When you do the shower walls, I would follow these steps:

  1. Make sure your wall is waterproof - good suggestions from @Shimon Rura.
  2. Install your tiles.
  3. Apply two thin coats of penetrating sealer. Leave each coat on for at least 10 minutes before wiping off (or follow the instructions).
  4. Grout the tiles, using sealer instead of water in the grout.
  5. Clean the tiles very well, allow to dry. Apply two more thin coats of finishing sealer.

If you're using the glossy sealer this might be a bit much. I would use the clear penetrating kind for the pre-grout coats.

The pre-grout coats are not strictly necessary, but do serve two purposes. The first is that if you have porous tile it will give you the extra protection you need. The second is it makes cleaning up the grout easier if you're sloppy. Adding sealer to the grout is supposed to help with bonding it to the thinset - not sure if that's true, but if you have extra on hand it works fine.

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