Waterproofing a shallow window jamb

[aaronk]

Hi, everyone.

I've seen a few posts like this while searching for an answer, but I can't find one that's quite like my needs.

I am renovating my bathroom and I have a window that needs to be waterproofed. The window itself is almost new (installed last year), but the jamb around it is original wood. That is what I need to waterproof. The problem is that there's very little space to do so; only about 1/2". How do I waterproof this?

I've already heard that I should apply caulk between the cement board and the window jamb, but then what? When I Redgard the shower, do I also apply Redgard or Kerdi membrane directly to the wood jamb? If so, how do I attach it? Thinset? If not, what should I use? Once that's done, how do I hide it? I obviously don't want a nice red outline to my window once tiling is complete. Do I put thinset and tile over it? If so, do I put tile all the way around the window jamb, including upside-down at the top of the jamb?

I guess I don't really know where to start.

Thanks in advance.

[Carbidetooth]

I suspect you don't want to hear this, but what you've got is a replacement vinyl window installed in and old wood window frame. My guess is 40's-50's house.

IMO getting this to a place where it can be effectively waterproofed will mean removal of wood frame and either reduce rough opening to fit existing vinyl window or replace vinyl window with one fitting rough opening remaining after the wood frame is removed.

Anything less than above has too many unknown quantities to make me feel confident in a waterproofing strategy. The old frame is a wild card.

[rmckee84]

I agree

[aaronk]

Yeah, ouch. If I did that, would that also mean installing new cement board to go right up to the vinyl?

[aaronk]

This window is the same size as many on my home. I may be able to get the person who installed this window to remove it and place it in one of those frames (where it won't be a problem) and install a slightly larger one here.

[SpaceCadet]

Your window but a few thoughts.

Why do you want a bigger window in the bathroom? I'm assuming this is in the shower or tub surround because you want to waterproof it. Why not replace it with a smaller cheaper vinyl unit that will be made to sit higher up and get less exposure to water and wall up the space underneath it. Don't know what the code is where you are but around here it has to be tempered glass anyway and you may or may not want that frosted.

If you're not married to having a window, why not remove the window entirely, wall up the whole thing and save yourself a waterproofing hassle? Natural light is nice but a bathroom fan works better at keeping the humidity down anyway.

If that's a 2x4 wall, that must be a replacement window that goes inside the frame and is held in place by trim. If you get one with a flange that goes over the outside sheathing of the wall, you'll have more space inside, probably around 2". Plenty of space to run cement board up to the window. It's more trouble to replace since you'll have to do something with the outside trim and siding but it's probably the all-around better way of doing it.

[huskerfan-23]

My situation is exactly the same. I was advised to fill up the whole wall with Plywood (1/2) and then put kerdiboard on top of the plywood (essentially, the plywood would be where your cement board is right now).

That creates a little bit of a return on the window, and I called schluter and they said to cut some of the kerdi board and place around the window adhering it to the wood with kerdi fix. They said a suitable bond can be made to wood. They then advised to wrap the entire window with kerdi membrane.

They also made a great suggestion that I had never thought of. They said if the return is too small to tile, I might be able to put a schluter transition in around the window (on top of the kerdi membrane). They thought the schluter schiene-step profile would cover the small return on the window. Of course, this would need to be 100% siliconed around the window.