- Oct 2, 2019
- Reaction score
- Alabama – Left California 2020
There's a guy on youtube that that did two videos...The first one he rabbited the cement board and went over the flange to about 1/8" about the pan. In the second video, He stopped at the top of the flange with the cement board and filled in the flange area with thinset, then fiber tape and then more thinset.The cement board could go on top of the flange and you can seal the gap with caulk before applying the waterproofing. This makes it a continuous water proof membrane that ought to prevent water from ever even getting to the cement board. If you are using 1/2" cement board and depending on the size of the hook, you could make a cut on the bottom of the cement similar to that in a rabbet joint so that it slides a bit further down and over the hook. In my case, I went with the first case but, since I had a cast iron bathtub, if cut the rabbet only at the places where the board went over the screws so that it could reach closer to the bathtub while minimizing the bulge because of the screws.
Another guy does a similar thing with the gap at the flange
I agree...it sure doesn't seem like these guys above are leaving a gap though. I'm concerned with hanging the tile down over an 1 1/2" gap with nothing behind it. If I did the method of filling it with thinset (like the videos above) it would be touching the pan. I could paint Aqua Defense over it (like they did) and then tile to 1/8" above the pan and fill it with caulk.By way way, when you put the tile, just leave the gap behind at the bottom and don't put mortar on the tile in this part. The gap prevents water from getting wicked upward through capillary pressure.
Agree!And, as far as I know, you *really* don't want grout at the bottom, especially with an acrylic shower pan (or bathtub). They flex slightly with load due to our weight, or filling up with water in the case of a bathtub, and you want to use silicone there because of its flexibility. For the same reason, the tile should not be touching the pan or it will squeak as the pan rubs against the tile with movement.
I was researching a little about vapor barriers. A discussion on Terry Love Plumbing (God Rest His Soul) came up
Terry Love Plumbing Forum
Q. Do we need to put plastic vapor barrier behind durock cement board ?
You want exactly one vapor barrier layer on your wall. So if you are using a surface applied waterproofing (which would also be a vapor barrier), you don't put any vapor barrier behind your cement board. That also means that if you have fiberglass batts in the stud bay behind the cement board, you use unfaced batts.
I am more confused..now this bathtub/bathroom has one exterior wall and 2 interior wall ..
On the exterior wall there is fiberglass insulation which has brown paper on it ..(so thats faced batt correct?) so on this wall when we put durock cement board - we dont put redgard or kerdi memberane and neither plastic vapor barrier?
because that brown part (face) will take care of it?
No, brown paper batt facing is not waterproofing. So you need the Kerdi or redgard on the inside of the cement board as waterproofing.
But since that waterproofing is also a vapor barrier, and you don't want two vapor barriers in the same wall assembly, you also need to replace the face batts in the exterior wall with unfaced batts. You may be able to just peel the facing off the batts. And you certainly don't want to add plastic behind the waterproofed cement board.
Yes and yes.
Typically for the silicone you'd use a caulk that is color matched to the grout you are using, most grout manufacturers offer that.
Just confirming last thing ..both tile and cement board will sit 1/8" above the tuck deck correct? and that area to be filled with silicone?
That would be in accordance with the diagram, although you don't fill the area, you install a bead as shown. I don't have a strong opinion on the gap height of the cement board above the deck.
Rather than tear off the paper face, it is acceptable to take a razor knife and put some slashes through it. THe idea is you don't want to trap moisture in between multiple barriers. WIthout the paper, the insulation may slump down, leaving gaps at the top.
My personal preference is to use a surface waterproofing material, and while some prefer a paint on one like RedGard, I like a sheet membrane like Kerdi. It's harder to get a proper waterproof layer with a painted on one without pinholes, runs, or thin sections. Too thick is just as bad as too thin, whereas, with a sheet, you need to ensure the seams are done right, and with the required minimum overlap, there's extra protection there. Normal cement board is not waterproof. One of the foam-core panels work, too, but there you have seams and screw holes to waterproof. Not hard, but required in their systems.
Do You Need A Vapor Barrier Behind Cement Board?
Keep in mind that your wall must only have one vapor barrier layer. There are cement boards that are already equipped with waterproofing material. Thus, if you add a vapor barrier behind it, it will just trap the moisture.
So the moral of the story is; Use just one vapor barrier. I'm going to use Aqua Defense (Red Guard like membrane).
Thanks havasu!Chalk, or caulk?