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Old 10-08-2018, 04:00 AM   #1
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Caulking Deep Gap Between Bathtub and Wall


I am brand new to this forum and to DIY-ing. I removed old caulking around the tub, exposing gaps (about 10"+ inches deep and 1/4"+ wide).

These gaps run vertically where the outside side of the tub meets the tiled wall. That is, the gap runs vertically along the facade of the tub which faces the rest of the bathroom, not along the inside perimeter of the tub.

I hope this makes sense. I am not able to post pictures, as new users are not allowed to do so until they make three posts. This is my first post.

I have to sets of questions: First, how to address the width of the gap? Second, how to address the depth? The advice I got from the online source and from Home Depot employee is contradictory.

1. The gap is 1/4" wide and even a bit wider at the top. What technique should I use to bridge that width? I read online that for gaps between 1/4" and 1/2" wide, one should apply two beads of caulk, one along the edge of the tub, the other along the edge of the wall. Then one should smooth the caulk with wet finger to join the two caulk beads. Is this what I should be doing?


2. The problem the gap is not only wide but very deep (10"+). The instructions I read from the same online source also suggested that if the gap is deep, I should not follow the method outlined above. Instead, I need to stuff backer rod (flexible, non-porous foam tubes) into the gap so that caulking does not prolapse into its depths.


A Home Depot employee advised me that deep gaps like that are not a problem and not use backer rod but just stick with silicone caulking for bathroom. Should I listen to Home Depot or to the online source and
install the backer rod?

3. If you recommend backer rod, what technique should I use to apply the caulking over the backer rod (or similar product you may recommend)? I have read that I should push rod into the gap so that it fills it completely, its top just below the surface. Then squeeze caulk onto each side of the rod where it joins the tub and where it joins the wall. The instructions did not specify whether or not I should run my finger between the two lines of caulk to join them but I assume that I should.

4. If you recommend I skip the backer rod, what technique should I use to apply caulking so it does not prolapse into the gap?

5. Should I use 100% silicone caulking for bathrooms or something else? For example, I read from the same online source that for gaps wider than 1/8" I should use sanded caulk. I didn't even know there is such a product, as I am only aware of sanded grout. Perhaps this is what was meant?

Thank you in advance for your wise council.

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Old 10-08-2018, 05:46 AM   #2
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RedGard to Repair Chipped Board Behind Broken-Off Tile?


I am new to this forum and to DIY-ing. One of the tiles (approximately 3" x 6"), abutting a 90 degree corner, came off from the wall surrounding the bathtub. The shower and faucet are mounted on the same wall, so this wall gets a fair bit of moisture. The board underneath the tile has a gray, slightly rippled/textured thin layer. This layer is chipped in a few places and these chips allow me to see white substance underneath the gray layer.

I was worried that the chinks in the board would allow the moisture through. So, I primed it with RedGard (1:4 solution) and, after it dried, applied two coats of RedGard at full strength using fiberglass tape embedded in RedGard to cover the chips in the board.

I also detected a hole in the same spot where the tile came off (i.e., in the corner joint, just above the lip of the tub). This hole extended past the board, far into the gap behind it. I used fiberglass tape and RedGard to close it off as well as some other narrow gaps in between the two walls joined at a 90 degree angle to each other.

The effect is that the board behind the loose tile as well as the gap where the two shower walls meet next to this "naked" bit of the board is now sealed against moisture.

1. I now wonder whether or not I did the right thing. By sealing off the small "naked" surface of the board (about 3" x 6") and the gaps in between where two walls meet behind the broken off tile, did I prevent moisture from wicking off effectively?

Will moisture now gather behind the tile I plan to install back in its own, newly waterproofed, spot?

2. If so, should I puncture the RedGard film in a few places to let the moisture through before I apply thinset over RegGard to re-attach the tile?

3. I have read on this forum in one of the other threads that AcrylPro is not going to adhere to RedGard and that I people should use thinset, such as Versabond or even more pricey Flexbond. I do not particularly want to have to mix Versabond but I am assuming there is no premixed thinset--equivalent to Versabond--that would bond well to tile?

Thank you in advance.
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Old 10-08-2018, 10:20 AM   #3
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Hi Sam, Do not use any "pre-mixed thinset." The wording is misleading to deliberately catch newbies off guard. Use VersaBond. You don't need FlexBond.

On the caulking, use silicone. Your problem is that nobody installed wood backing for the sides of the tub. If you are going to tile over that area you can fill it with anything . . . or not fill it at all. Tile it and then use silicone caulk between the tile and tub to keep the small amount of water out that might get on it.
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Old 10-08-2018, 12:13 PM   #4
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RedGard to Repair Chipped Board Behind Broken-Off Tile?

John Bridge,

Thank you so much for answering my questions!

I would like to clarify a few things since I am quite new at this.

Is it OK that I sealed the board behind the one tile that came off with RedGard or is it going to prevent moisture from wicking off?

If it is going to prevent moisture from wicking off, should I puncture a few holes in RedGard coating, especially in the part where I used fibreglass tape + RedGard to seal across the corner joint? (The missing tile is abutting the corner).

Thank you!
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