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Unread 01-22-2019, 11:39 AM   #1
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2 layers of hardiebacker, both aquadefensed

I installed new hardiebacker, taped & thin-set, and applied 2 coats aquadefense in my tub/shower in preparation for tiling next month.

I should have shimmed the back wall (right side of shower entrance), because the existing 60 y.o. gyp. bd. that I'm meeting is 1/2" thicker than my hardiebacker. I'm considering eating the cost and simply installing a whole 2nd layer of backer to that side in order to be flush with existing gyp. bd. before tiling the shower. I will ofcourse, be applying aquadefense to the 2nd layer.

My fear, though, is having 2 barriers of aquadefense sandwiching in any moisture that may make it's way into that 2nd layer.
Can anybody tell me if this is cause for worry?
Thanks so much in advance.
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Unread 01-22-2019, 11:50 AM   #2
Yes si
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Hi Eric.
If you’re going to be using 3/8 thick tile on the wall after thin set it’ll make up the difference if not it’ll come real close.
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Unread 01-22-2019, 01:07 PM   #3
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One possibility would be to rip out the drywall, and extend the backer and tile.
You could also either replace the drywall with a thicker drywall and repaint, or use drywall mud to feather the difference between the tile and the drywall and repaint.

If you want to go the route of an additional layer of backer, try pulling the Aquadefense off the existing layer.

What I discovered (by accident) while using Aquadefense in my bathroom is that dried Aquadefense will stick to itself better than it will stick to backer. Once you get a small piece dried Aquadefense cut and peeled up, the rest of the Aquadefense will just keep peeling as you pull on that small piece... likely in a nice circular spiral until you either cut the strip or the strip has run all the way to the edge of the wall.
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Unread 01-22-2019, 04:42 PM   #4
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Depending on the thickness of your tile, it might just come about flush as indicated. If the tile's top surface was even with the drywall, you wouldn't have to deal with the expense of bullnose or a profile to finish it off if you kept that stack nice and straight.

If you want it flush with the drywall, you might find it easier to just trash that layer and then shim, and add a new one. If you coated thing properly, it probably won't hurt to just put a second layer up then seal it to the remaining wall, though. The cbu is not going to transmit much water vapor through the waterproofing layer then the board to then get 'stuck' in the sandwich if you seal things well. If you can remove it, that might be best, though.
Jim DeBruycker
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