First of all, is my terminology correct? These are brands of synthetic wood alternatives:
- #Wedi
- #Qboard
- #Schlüter #kerdiboard
etc.
Is “construction board” the generic name for this stuff? I think some people call them “building panels”. I ask because my search for Invidious (Youtube) vids came up short. I would rather not have a brand-dependent search query because I have to try many queries as it is to try to get this answer.
Qboard offers a factory made corner piece (called Qorner; attached to this post). I was trying to work out how I could do that myself. I’ve never worked with #constructionBoard, nor have I used a router, but I suspect they use a router to cut a “V” in the board without competely bottoming out (but nearly), so the outer skin does not get cut. Has anyone done this?
I actually have used Wedi in a couple projects. I am not an expert or professional but will share what I know.
The stuff is essentially sturdy foamboard and can be cut with a razor knife, no power tools needed. It is critical that the entire system be fully sealed and waterproofed, with all joints sealed with the provided wedi sealant. (I used the stuff provided in caulk tubes) While you could cut a V and bend the board, I would not trust it to be waterproof and you would need to seal it with the sealant anyway , so it would probably be stronger to just do a butt joint with sealant.
While I would generally never recommend on planning on anything being accessed from inside the wet area, wedi sealant might work to your advantage because you could probably cut out the box along a sealant joint, replace the part, and then re-seal the box to the location with new sealant.
I’d check the wedi documentation for the correct joint details. I’m not sure exactly where your box will be and if it will have standing water against it, but if so the details might be different or even not at all recommended.
Hope that’s helpful.
Thanks for the feedback.
I think this is where the different kinds of boards differ. Some tests¹ demonstrate Wedi is not waterproof but Schluter KERDI and another brand is. This guy says KERDI board can be scored and snapped to fit into a car, and unfolded at installation and it maintains its waterproof properties.
If I opt for foam board then it would probably be Wedi so indeed it would theoretically need a waterproofing system on top. I say theoretically because I don’t think the shower is waterproof to begin with (it’s apparently tile directly on concrete rendered over brick). But I should still probably practice doing it right.
I’ve noticed construction board is fastened using a big washer of sorts and a screw through it. If the board is 10—15mm thick and I use those washers on a corner, they would overhang. I suppose I could cut the overhung portions off with an angle grinder. I’m also unclear on how strong the joint is if a screw is driven just into the foam to fasten the butt joint. Wouldn’t the screw pull out without much force? Perhaps I’ll use a 2×3cm piece of wood on the inside corner and screw both boards to that since I have that wood on hand.
Or when you say “with sealant”, do you mean no screws and sealant alone?
You wouldn’t use fasteners in the joint itself, and you’re exactly right that they would pull right out. The screws are used to fasten through the face of the wedi board to wooden studs behind it to provide strength, and then the penetrations and joints are all sealed with the wedi sealant. The board itself is waterproof, you’re only sealing the joints/penetrations. I believe that small shower niches with 1/2” board are sturdy enough that they don’t even need wooden framing and just rely on the board+sealant, but am not sure on that.
I’m not sure if this is the latest version, but this technical document has a ton of information: https://www.masterwholesale.com/media/wedi_Technical_Handbook_January_2021_Digital.pdf