Where Backerboard meets tub

[Biegrod]

I am in the process of replacing the wall surround above and all the way around an existing fiberglass (or some sort of plastic) tub. The original surround was 4" tile over greenboard and (according to the inspector when we bought the house) the window sill in the shower area leaked water because it was tiled and not a solid marble sill.

The greenboard is gone, I have placed concrete backerboard on the back and the long side of the tub. The tub has about a 1/2 - 3/4 in "ridge" on the three wall sides that the backer board is resting on. The backerboard is screwed into the studs with the mfg.recommended screws. The next step is the thinset and taping.

OK, so here is the question: Do I fill the gap between the bottom of the backer board and the tub surface with thinset, tub caulk, or what, again its about a 1/2" high by 3/8" deep area to fill.

Finally, once filled, I will be using large (either 8x12 or 12x12) tiles. should these be set all the way down to the tub surface level or should there be a gap for caulk or ????

Thanks for any help you can provide.

~Bieg

[jadnashua]

Bring the tile down to about 1/8" of the tub surface. Caulk all changes of plane (i.e., the corners) and changes from one material to another (i.e., at the tub edge to the tile). It sometimes helps to fill the tub with some water prior to caulking in case it settles. Around the windowsill, maybe 8-10" all around it, buy something like RedGuard (available at Home Depot and other places where it may be cheaper) and paint it on per the manufacturer's instructions. This stuff is a waterproofing paint. Moderately expensive as paint goes, but it is cheap insurance. Once it dries, then you can put the tile up over it and, with the RedGuard under it, you can tile the sill if you want. It is red and kind of thick, you can brush, roll, or trowel it on. Since it will be covered up, it doesn't matter much what it looks like as long as you cover things well. BTW, I learned this reading stuff at www.johnbridge.com and I'm not a pro. Depending on the tile, make your grout line appropriate (some tile are not very consistent in size from one to the other and it is hard to hide this if you use a small grout line). For grout lines >1/8", use unsanded grout, for 1/8" or greater, sanded is usually used, otherwise, if you use unsanded, since it shrinks some when it cures, you'll end up with cracking. Once everything is cured out, depending on the manufacturer but usually a week or so, put a good penetrating sealer on the grout.

[jimbo]

Your backer board is NOT installed correctly. It should overlap the tub flange and stop about 1/8 to 1/4 " above the tub deck. If you proceed as is, you must caulk that joint extremely well because it is an invitation for water to seep through there.

[maddiemom6]

Ok.. I am sitting here with four tile books in front of me and the John Bridge forum open... they all say that the cement board should come just to and not quite touching the top of the plastic lip. This is also the way they show to do in on the John Bridge site. Now.. I do have a 5th book that is REAL old and they show "green board" lapping over the side of the lip for a tub...but this book is a "Sunset" book that is over 20 years old. So while it might have been done that way.. I am pretty sure that newer methods have evolved but am also sure than some still do it the old way. You got to wonder sometimes how often old and new advice compete..but in this case I got to go with John.. he is the master ( but he does not like plastic solid surface bottom in the first place as far as I can tell)

Maddiemom6

[jadnashua]

Ideally, you either notched the studs so that the lip was flush with the stud and you could have run the cbu down near the top of the tub (or, you could have shimmed the cbu out so it could run down near the top of the tub). But, doing it the way you did, you still run the tile down to about 1/8" from the horizontal tub edge, then caulk it really well. The bottom edge of the tile will not be supported, which is not ideal, but since you aren't walking on it, I don't think it will be catastrophic. My unprofessional opinion.