CBU to Drywall Transistion

[rwbil]

Redoing bathroom and trying to figure out the best way to transition from the CBU to Drywall. Attached is a photo. I drew blue line where tub ends as not clear in the photo.

Thinking of taking CBU past the tub to the drywall and then using joint compound, but the CBU is not smooth and not sure how smooth I can make it and paint it and it look right.

Maybe I could use a smoother CBU.

If I take the drywall up to the CBU at the Tub and use Thinset on the transition, I cannot see how I can paint that and it look right.

What is the best option.

[cx]

Robert, you really want your CBU, and your waterproofing, to extend past the tub and down to the floor.

As I see your photo, you can easily finish the CBU/drywall joint with drywall tape and mud and finish it to match the wall. A smear of drywall mud can make your CBU surface the same as finished drywall.

My opinion; worth price charged.

[rwbil]

"A smear of drywall mud can make your CBU surface the same as finished drywall."

I can see that if I use the smooth side, but the cement board says rough side for Cement and Smooth side for mastic.

Is it OK to use the smooth side for thinset that way it would be easier to cover with joint compound and paint.

[PC7060]

Simply apply mesh tape over the joint between the backer board and drywall and then mud with drywall compound like any other drywall joint. I’ve posted a pic below which shows a mudded backboard to drywall joint.

As CX mentioned, it’s best to extend the backer board past the wet area. I’d take the backer board out to meet up with the drywall you showed in picture.

Once you’ve got the surface taped, skim coated and sanded you can prime it and tile over it to your desired end point.

[cx]

You can use either side, Robert, for either purpose.

My opinion; worth price charged.

[Shady at Best]

Agreed. I run my cbu, kerdi board, and even wedi a few inches outside the wet area and finish it the same as I finish sheet rock. I have even ran out of sheet rock and brought the kerdi board 3 feet outside of the bathtub and skimmed it with drywall topping and sprayed texture. IT was good to go. The drywall/sheet rock compounds and plastering compounds bond well with most if not all types of tile backer.
Robert, I see that the valve is loose and not installed yet but I want to see the hot water line secured before you cover that wall up
I like using spray foam on pex to hold in place when its in an areas where the clips will not work

[rwbil]

Installed the smooth side out on the wall that ties into the drywall as shown in the photo.

My next question is about waterproofing.

I ran the CBU above the tub lip. This is an old cast iron tub and it barely even has a lip. I also put flashing tape (show by blue arrow) behind CBU to the tub lip to stop water from getting behind the CBU.

Also planning to Redgard.

My question is if water were to get behind the subway tile, how would it escape? The bottom of the subway tile will be caulked. And I am certainly not going to leave weep holes with that little tub lip.

Does one supposed to plan for water exit or is the amount hopefully either nothing or so small just dont worry about.

Lastly, this time I want to get a Telescoping pole for my laser to align up the Subway tiles. Any suggestions on things to look for.

[ss3964spd]

Has been discussed here before, Robert, just how does any accumulated water escape, no real consensus that I recall. But with roughly a bazillion tub showers having been built with that tile to tub joint being fully caulked it would seem it's a non issue. If I ever manage to get my shower/tub walls tiled I'll probably leave a few weep holes strategically placed.

Sorry, no suggestion on the tele-pole question.

[boberic00002]

As far as how to support a laser level, I picked up a tripod at a thrift store for like $5.

[rwbil]

Rehabbing my bathroom and just installed the CBU as shown in the photo. Next plan to thinset and Redguard.

I understand one needs to thinset the vertical joints as the wall studs are 16" apart and the thinset helps to make a stronger structure wall.

But the horizontal corner joint already has studs in the corner and I don't see how thinset will make that corner any more structurally sound.

Just like I am not going to thinset my niche as I dont see any reason one needs to.

Can one just Redgard with fabric the inside corners or is there a reason why the inside corners must first have thinset applied.

[jadnashua]

RedGard won't bridge a gap, so if you follow the instructions, yes, you want to tape and thinset all joints, let that cure the minimum time they call for, and then coat with the RedGard.

Do yourself a favor and go to a paint store and pick up a wet film thickness gauge and read up and understand how to use it. Too thick (hard to do) is just as bad as too thin coats, and you don't really want to just keep adding coats as that can lead to its own problems.

[rwbil]

Not sure why it is different than what I plan to do for the Niche. Caulk the little gap, apply Redgard, put on the Redgard fabric and apply Redgard over that.

I bought the thickness gauge when I bought the Redgard.

Just seems a lot less risk of lippage not using thinset and I am still not convinced thinset is needed in a corner.

[cx]

Robert, it'll help if you'll keep all your project questions on one thread so folks can see what you're working on and what's been previously asked and answered. A moderator can give it a more generic title any time you'd like to suggest one.

The best reason to treat the CBU joints the way the product manufacturer calls for is because the manufacturer calls for it. You don't like their installation procedures, you're certainly free to install in any manner you think best.

My opinion; worth price charged.

[Tiger Mountain Tile Inc]

Mesh tape and thinset the two inside corners and the seams and all the way around the niche. It ties it all together. Then waterproof. Caulking the corners isn't the right way of doing it.