I inadvertently chipped away too much mortar bed, exposing the bituthene waterproofing underlayment, while replacing a slate tile on my deck. I'm not sure whether to repair with additional thinset mortar when I lay the new tile or apply a silicone roofing sealant before the thinset.

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  • "exposing?" or "cutting a hole in?" - kinda makes a huge difference here. – Ecnerwal Jul 7 '17 at 14:49
  • The tarpaper wasn't torn, but rather I was able to remove the loose mortar, exposing the tarpaper below. – Grant Jul 7 '17 at 15:00

If you have not punctured/pierced the membrane, fill it with mortar/thinset and tile away.

  • I noticed that the membrane had inflated due to the hot weather. A little bit of oozing of tar was noticeable too. Wouldn't it be safe to cover the membrane with a silicone roofing sealant before laying the thinset? – Grant Jul 7 '17 at 18:36
  • If doing anything with a bituthane installation (which is not tarpaper) your best, most compatible, bet would be to carefully expose a larger area, clean it carefully, and apply a patch of bituthane, rather than tossing some sort of silicone sealant at it that probably won't bond nearly as well. Bituthane is designed to stick very well to itself. – Ecnerwal Jul 8 '17 at 13:43

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