So, we bought a house with the intention of doing most of the finishing levels of renovation ourselves and hiring to have structural work done.

The contractor put up cement board after repairing some water damage in the old bath/shower wall (window had so much water damage it was literally dirt with an earthworm in it!). The plan was they would get the surface ready for us to come in and tile.

So, cement board is up, they applied AquaDefense and called it good.

Here's my question, I know they did not shim out the studs and level the walls, and they also put tape on the joints but did not thinset the joints pre-waterproofing. Also, we didn't have drywall up yet (there was an asbestos discovery so everything went to studs - surprise) so they couldn't thinset the transition between sheetrock and cement backer board.

So, I am going to be doing a lot of leveling and feathering out with thinset on top of AquaDefense- which is fine. Here is my question:

If this had been done 100% correctly it seems like a lot of this thinset skimcoat work would have been done under the Aquadefense, then Aquadefense, then a layer of thinset to get the tile to adhere.

Should I do another layer of aquadefense after I make the surfaces nice, since there are some spots that I am worried about leaks on (joint between sheetrock & cement board, cuts around trim openings (they're a little big and I'm going to thinset on some waterproof collars for the pipes)? This would mean our layers would be cement backer + aquadefense + thinset skim coat + aquadefense + tile mastic - I'm not sure if that is a terrible idea or necessary to make sure we have a level surface that is also definitely waterproof.

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    Commented Jul 19, 2022 at 18:44

1 Answer 1


Yes absolutely because in between the seams there are voids that the thinset will cover which never had waterproofing. I think a skimcoat shouldve been applied prior to waterproofing

  • 1
    You're answering a 9-month old question. That bathroom got finished up a long time ago and is leaking into the walls as we speak. The seams should have been finished with tape and thinset. Commented May 1, 2023 at 16:23

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