Replace ONE large tile (and substrate) on shower wall

[Paul Reece]

My best access to the faucet/filler plumbing of my bathtub was through the wall of the adjacent shower stall.
That wall is tiled with large 12 x 24 ceramic tiles. I was successful in cutting out one complete tile and its substrate (something similar to Durock) without damaging surrounding tiles, but now that my renovation to the plumbing is done, I have to rebuild that opening. I face a series of challenges, and a couple of them leave me uncertain.
1.) I have augmented (not shown in photo) the framing members I found inside the wall to assure generous, rigid support for the 1/2" Durock I will use as replacement substrate. But since the edge seams of that replacement panel will exactly coincide with the eventual grout seams around the replacement tile, I want to be sure it offers no opportunity for leakage into the wall. Seam tape appears to be kinda pointless since I can't bridge the gap between the old Durock and the new (only one side of that gap is accessible). I thought I might squeeze caulk into the joint and rub it in as deeply as possible while smoothing it to flush with the Durock surface.
2.) It's such a small replacement job, I thought I might use a pre-mixed mastic to adhere the wall tile, but it's such a large single tile at 12 x 24, I worried about the mastic setting up properly and/or in a reasonable span of time. Adhesives sandwiched between cement board and ceramic tile don't encounter an arid "drying" environment, and from what I've read about mastics, they don't have an actual "curing" process.
Any thoughts and recommendations will be appreciated I'll wait for advice before commencing the repair.
(Photo is part of a Facebook post from back when I was much more enthusiastic about this whole project.)

I sistered that stud on the left by sliding a 12" upright around it to the far (left) side, snugging it up to the back of the substrate and screwing through the two members.
I installed secure, rigid horizontals across the opening at the top and the botom, snugging them up to the backside of the original substrate and sharing the width of the lumber's bearing surface half-and-half between the old Durock and where the new Durock will be. Then I put an upright between the top and bottom crossmembers.

 

[wwhitney]

1) What is the waterproofing method on your shower? Fundamentally it seems impossible to fully restore the integrity of the waterproofing layer on that shower wall. Grout and tile always allow some water to pass.

If there's no water proofing between the cement board and the tile (e.g. a membrane layer like Kerdi or a fluid applied layer like RedGuard), which is a poor but common practice, then you should at least be able to restore the cement board to as good as it was. I'd suggest cutting the new cement board to 1/16" undersize on all sides, and then filling that gap with a generous amount of a sealant like Kerdifix.

You could then fill the screw locations flush with thinset, and apply two coats of fluid applied waterproofing. But there's no real way to reliably tie that into any waterproofing behind the rest of the tile.

2) Absolutely do not use mastic to set your wall tile. While some manufacturers allow that application, it's always a bad idea. Particularly for 12x24 tiles, for the reasons you've identified.

Cheers, Wayne

 

[Sponsor]

 

[Jadnashua]

Industry calls for a moisture barrier on the walls of a shower. That can be a simple sheet of plastic behind the cement board or roofing felt, or, it could be a topical waterproofing, whether a sheet membrane, liquid, or a tileable foam panel instead of cement board like KerdiBoard, or WediBoard. If you were to use one of those to fill the hole, since you can't do any overlap, I'd use KerdiFix on the joints and screwholes, or if using WediBoard, their proprietary sealant.

Since you can't really get a moisture barrier behind the wall, I'd be more tempted to use KerdiBoard or WediBoard. If you've got any local distributors, and they have a sheet with a corner broken off, they may sell it to you cheap, or maybe even give it to you.

Do not use mastic...most of them do have a maximum tile size limitation, and I'm pretty sure yours exceeds that. Lowes sells a 10# box of thinset, so you don't have to buy a whole bag and then throw most of it away. Watch the date code...you don't want any thinset older than a year, or if the container is not in good shape. Depending on the brand, you might need to call them to decode the date. Some are written in plain info, some are coded.

 

[Paul Reece]

1) What is the waterproofing method on your shower? Fundamentally it seems impossible to fully restore the integrity of the waterproofing layer on that shower wall. Grout and tile always allow some water to pass.

If there's no water proofing between the cement board and the tile (e.g. a membrane layer like Kerdi or a fluid applied layer like RedGuard), which is a poor but common practice, then you should at least be able to restore the cement board to as good as it was. I'd suggest cutting the new cement board to 1/16" undersize on all sides, and then filling that gap with a generous amount of a sealant like Kerdifix.

You could then fill the screw locations flush with thinset, and apply two coats of fluid applied waterproofing. But there's no real way to reliably tie that into any waterproofing behind the rest of the tile.

2) Absolutely do not use mastic to set your wall tile. While some manufacturers allow that application, it's always a bad idea. Particularly for 12x24 tiles, for the reasons you've identified.

Cheers, Wayne

Just the sort of guidance I was looking for. Many thanks, Whit. You've identified some new products and priorities.

 

[Paul Reece]

Industry calls for a moisture barrier on the walls of a shower. That can be a simple sheet of plastic behind the cement board or roofing felt, or, it could be a topical waterproofing, whether a sheet membrane, liquid, or a tileable foam panel instead of cement board like KerdiBoard, or WediBoard. If you were to use one of those to fill the hole, since you can't do any overlap, I'd use KerdiFix on the joints and screwholes, or if using WediBoard, their proprietary sealant.

Since you can't really get a moisture barrier behind the wall, I'd be more tempted to use KerdiBoard or WediBoard. If you've got any local distributors, and they have a sheet with a corner broken off, they may sell it to you cheap, or maybe even give it to you.

Do not use mastic...most of them do have a maximum tile size limitation, and I'm pretty sure yours exceeds that. Lowes sells a 10# box of thinset, so you don't have to buy a whole bag and then throw most of it away. Watch the date code...you don't want any thinset older than a year, or if the container is not in good shape. Depending on the brand, you might need to call them to decode the date. Some are written in plain info, some are coded.

Okay, guys. Mastic is DEFINITELY off the shopping list. Thanks for the tip on Lowes, Jim. The only reason I was trying to avoid thinset was the apparent requirement to purchase it by the ton. Your advice dovetails perfectly with Whit's, so I'm off to a good start. Nothing I can do about the absence of a barrier behind the Durock, that problem is universal in the existing build... and less of a problem in this specific location (a low-splash area) than in the rest of the shower. It's members like you two who make the Love site my starting point for DIY tips and help. Bless ya.

 

[kevreh]

I would use a foam board product like the mentioned wedi, Kerdi, or goboard, No need for a vapor barrier since their waterproof.

The key is how do you prevent water from seeping into the seems around the board? What I would do is leave a 1/8” gap around the board then seal it with a silicone caulk or a quality sealant like Kerdi fix or liquid nails fuse-it. Then use a modified thinset to adhere the tile and grout.