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I have shower tiled with travertine and along the entire bottom a thick almost rubber-like substance is slowly leaking out. It is a grey / black color. I'm assuming it is thin set that wasn't mixed properly and never completely set up. Should I be concerned, and if so what should I do about it?

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How long ago was the tile installed? You may want to add a picture or two to help figure out if it's mold or something similar. – alt Jun 23 '14 at 19:39
House was built 6 years ago but it's been doing it for a few years now. When I pull it out, the part that is under the tile does not appear to be moldy. I tried to post a pic, but didn't get it to work. Thanks – user23282 Jun 24 '14 at 4:56
Hi! It looks like you’ve accidentally created a couple of accounts. If you’d like to merge them (there are some advantages to doing so), the instructions are here. Welcome to the site! – Niall C. Jun 24 '14 at 11:47

I suspect that's butyl sealant that a lazy installer used to prevent moisture from wicking up behind the tile, avoiding a trip to the hardware store. You might carefully trim it off with a razor blade and cover it with what should have been used in the first place: "tub & tile caulk".

Thinset has only two consistencies: powdery when dry and concrete-like after exposure to moisture.

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Thin set that is not mixed correctly will cause the tile to lay funny. The water will evaporate once the mix sets off. If it had too much water I think your first sign would be the tile scrunching down into the hollow space below it.

If you have a Shower Door track, it could be the caulk or plumbers putty they used to seal that. Sometimes a bad batch makes into the stores and it breaks down when it is supposed to just stay pliable.

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Oh, and if it was put together 6 years ago and actually has a way into the wall board out side the shower down at the corners. It could be wall board that is leaking, especially if it the Chinese wall board they had a recall on which had lead mixed in it also. Could explain the Grey and Black substances... – Johnny G Jun 24 '14 at 5:30

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