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Old 04-23-2014, 12:03 PM   #1
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Gap at concrete backerboard to tub lip transition


I wasn't sure which forum to post this in, so forgive me if it is in the wrong place...

I am finishing my basement including a full bath, and have run into an issue where my concrete backerboard buts up to my tub lip. I was trying to follow an article from Family Handyman when I installed my tub and backerboard. Unfortunately, I realized that I messed up by not shimming the backerboard out so that it could lay over the tub lip. So, basically, I ended up with the following (essentially I used the 'short lip' method on a 'tall lip' tub):



instead of what is shown at the bottom of this:



So, my questions at this point are:

- What can/should I use to fill in the gap between the back of the tile and the tub lip? Can I just fill it in with extra thinset or grout? Could I use quickset mud? What about the plastic? Will it cause an issue?
- Should I just remove the backerboard, shim, and reinstall? (really don't want to do this unless absolutely necessary)
- Any other options to fix this?

Thanks in advance.

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Old 04-23-2014, 12:08 PM   #2
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Gap at concrete backerboard to tub lip transition


You run a bead of silicone caulk in that gap.

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Old 04-23-2014, 12:14 PM   #3
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Gap at concrete backerboard to tub lip transition


Quote:
Originally Posted by Seattle2k View Post
You run a bead of silicone caulk in that gap.
Thanks, Seattle2k. It's a pretty huge gap, though. I'm talking about the gap shown in red below (not the gap between the bottom of tile and the tub). Can I just leave that part empty, and caulk between the tile/tub gap? Will the grout stay between the tiles if there is nothing behind them in that area?

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Old 04-23-2014, 12:28 PM   #4
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Gap at concrete backerboard to tub lip transition


Fill that gap with thinset---then waterproof the wall--of full as you tile if a surface waterproofing will not be used---
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Old 04-23-2014, 12:34 PM   #5
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Gap at concrete backerboard to tub lip transition


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Originally Posted by oh'mike View Post
Fill that gap with thinset---then waterproof the wall--of full as you tile if a surface waterproofing will not be used---
Thanks, Mike. So, do you mean to just waterproof the thinset part that I filled in? Or do you mean to waterproof the entire thing? I already have plastic behind the backerboard (I have read that some of you disagree with this, but it is already done now, so...).
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Old 04-23-2014, 02:08 PM   #6
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Gap at concrete backerboard to tub lip transition


As a follow-up question, where would you cut the plastic vapor barrier? And would you do this before or after filling in the thinset?

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Old 04-23-2014, 02:48 PM   #7
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Gap at concrete backerboard to tub lip transition


I would go with 3, and cut before the thinset. The flat/straight edge of the notch trowel is for water proofing, spread the thinset with it over the whole area you are going to tile and then notch. Do a small area at a time until you get use to it. It should say this on the bag of thinset how to use it as water proofing.
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Old 04-23-2014, 03:23 PM   #8
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Gap at concrete backerboard to tub lip transition


Quote:
Originally Posted by ToHellWithUGA View Post
Thanks, Mike. So, do you mean to just waterproof the thinset part that I filled in? Or do you mean to waterproof the entire thing? I already have plastic behind the backerboard (I have read that some of you disagree with this, but it is already done now, so...).
I believe he meant for you to waterproof the whole cement board, but being you have the plastic behind the board, DO NOT waterproof the cement board.

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Old 10-08-2014, 11:34 PM   #9
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Gap at concrete backerboard to tub lip transition


I know this is an old thread, but work got busy and I am just now getting around to doing this tile. I have about 3/4 of the tile on the wall done, but I have a few questions before going any further.

Here is where I am at this point:



I have started to fill in the thinset as suggested earlier in this thread, but I want to make sure I am doing it correctly. Here is a close-up of the area that I started. I cut the plastic about halfway between the bottom of the backer board and the tub, taped the rest of the plastic back to the top of the tub, and started to fill in with thinset, basically sealing the plastic to the tub. Does this look right?

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Old 10-08-2014, 11:38 PM   #10
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Gap at concrete backerboard to tub lip transition


Another question: With the method that I used (sorta wish I used Redguard, but oh well), I need to allow the water to travel down the plastic and back into the tub, right? Is this going to inhibit that in any way?

Also, when I go to grout/caulk, do I caulk the tile/tub line, or grout it? If I caulk it, won't it trap water? I would really like to seal the grout and keep water out all together, but I'm not sure if that should be done with the plastic installed how it is. (My wife really wants the grout sealed, as she hates the how the grout in the rest of the baths never seem to totally dry out at the bottom, and eventually mildew)

Last edited by ToHellWithUGA; 10-09-2014 at 12:00 AM.
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Old 10-09-2014, 06:37 AM   #11
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Gap at concrete backerboard to tub lip transition


Yes, seal the grout--it helps keep it clean----caulk the inside corners and the tub/wall connection---

Unless something is very wrong--only a slight bit of moisture will ever reach the backer board--never a flow of water----
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Old 10-09-2014, 07:44 AM   #12
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Gap at concrete backerboard to tub lip transition


Cut your plastic as in your picture #2 or #3. Then caulk the bottom of the gap. There's no real need to do anything else. You haven't really screwed up here, it's fine.
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Old 10-09-2014, 10:00 AM   #13
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Gap at concrete backerboard to tub lip transition


Great, thanks for the responses, guys! Really appreciate it.

One more (hopefully final) question:

A contractor friend is telling me that I need to get Kerdi/Schluder seals for around the mixing valve and pipes, especially since my cuts in the backer board are too big. Is this really necessary? Neither HD nor Lowes have these in stock locally, so I would be waiting a week or so for them unless I find them elsewhere.

Here is a close-up of the mixing valve and faucet holes. Are these really that bad? If I'm reading the instructions on my shower kit right, the black plastic comes off anyway, so it really wouldn't be sealing up against anything.

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Old 10-09-2014, 10:07 AM   #14
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Gap at concrete backerboard to tub lip transition


Those are not bad at all. When you put the decretive pieces on simply caulk around them.
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Old 10-09-2014, 05:44 PM   #15
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Gap at concrete backerboard to tub lip transition


Those are OK. Personally, I think the Schluter seals are overkill on the showerhead, but they do come in handy down low by the valve and tub spout. However you can compensate. That black plastic thing has nothing to do with it. You will need to install the shower handle escutcheon and tub spout according to manufacturer's directions, and if not specified, I would also silicone the top of each (not the bottom - put the silicone on in a semi-circle around the top 2/3 of the circle.)

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