[bora492]

I'm remodeling my bathroom, and want to add height to the existing tile, then install a shower curtain rail. The tile currently ends at 56", and I want to bring it up to 8' around the tub. I'm just going up with more subway tile.

The walls are plaster, but I found the studs, and am ready to install the backer board. My question is about leaving a gap between the existing tile "cap" and the backer board, to dispel any moisture / condensation.

I will follow instructions: 1/8" gap between boards, fiberglass mesh and thinset at all seams, then follow with 2 coats Redgard.

I know it's not going to be exposed to huge amounts of water, so maybe it's not even important, but I thought I would ask for opinions. Thanks.

 

[Nealtw]

I think I would set the board in a bead of caulk on top of the tile. Maybe put red gard on the bottom edge of the board first.

 

[jeffnc]

The walls are plaster, but I found the studs, and am ready to install the backer board. My question is about leaving a gap between the existing tile "cap" and the backer board, to dispel any moisture / condensation.

OK, as soon as you say that, you're really off on the wrong foot.


Tile substrate needs to be waterproofed behind the tile, first. Basically you should be able to take a shower in there without tile even going up. There are basically 2 reasons to use tile in the shower. 1, it looks good, 2, it's easier to clean than backerboard. That's it.


You say you're following instructions, but you're not - there's no way you can properly seam and waterproof the junction between the new backerboard and the old tile rail or trim. Personally I'd use Kerdi membrane to cover that backerboard, but I know it's probably too expensive in the size you need to buy. First thing you need to do is caulk that bottom edge with a polyurethane sealant, like KerdiFix (which is very expensive, but you can find something similar - I use MasterSeal NP). Then coat with some waterproofing. I don't use them, but RedGard and similar. You're right at this height it's not a huge deal, but it can easily mold back there and remember backerboard isn't waterproof. Water can't damage it, but it can stay wet and that means the studs will stay wet.

 

[bora492]

Thanks, that makes sense. Caulk the edge, then RegGard, making the substrate waterproof. Then, mount the backerboard. Just learning as I go....

After that, I feel I should use fiberglass mesh and thinset on any seams, then coat the whole thing with RedGard.

One question if anyone can answer. The backerboard is about 6" short on length. I can cut a 6" strip and screw it to one stud. Or, I can cut 16" off the backerboard, and cut a 22" strip and screw it to 2 studs. Seems it would be sturdier to attach to 2 studs, but I could be overthinking it. Any thoughts? Thanks.

 

[jeffnc]

One question if anyone can answer. The backerboard is about 6" short on length. I can cut a 6" strip and screw it to one stud. Or, I can cut 16" off the backerboard, and cut a 22" strip and screw it to 2 studs. Seems it would be sturdier to attach to 2 studs, but I could be overthinking it. Any thoughts? Thanks.

If you're using 12x12 tiles or larger, it probably makes no difference. If using smaller tiles (you mentioned continuing subway tile), I would go the stronger route.