Cement board to drywall transition [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


View Full Version : Cement board to drywall transition

08-08-2019, 02:55 PM
Hi all, I am in the middle of a bathroom remodel and have a problem with the transition from cement board to drywall transition right outside the tub area and I am just not sure how to resolve it.. on one of the transitions there is about a 3/16-1/4” bevel or lip on the drywall ..so the transition is not flush. I only realized this after I already hung the cement board and completed a butt joint with Thinset on that wall..(I have cement board to the ceiling so there is1 3x5 sheet and another half sheet on top) otherwise I probably would have shimmed that area before I screwed in the cement board. I am not sure if the difference is too much to float using Thinset or if I have to unscrew the cement board and pop it out enough to get shims on the studs ... which may be a problem since there is already a Thinset joint on that wall.

What is the best way to resolve the difference between the cement board and drywall?

Also, I have my cement board going to the ceiling since I will be tiling up to the ceiling ..is it necessary to joint the cement board and ceiling with Thinset? This is an unfinished ceiling at this time ..haven’t primed or painted it yet.

Any advice would be much appreciated..This is my first tile job so I can use any help I can get.

Sponsored Links

08-08-2019, 04:16 PM
Welcome, Chris. :)

I think a photo or two may help a good deal here. Use the paper-clip icon above the Reply dialog box to attach photos from storage on your computer.

I'm primarily confused about the "1/4" bevel or lip on the drywall." Also where the joint actually falls "right outside" the tub area." Ideally that joint should be an absolute minimum of 2" beyond the face of the tub and preferably 3" or more to allow for waterproofing and tile in a "tub leg" all the way to the floor.

Not sure what you'd do with your tile if you did find a way to shim the edge of your CBU as much as 1/4" making it fall less than in-plane with the rest of your tiled shower wall.

08-08-2019, 04:38 PM
Thanks for the reply CX! I’m including a picture to help explain what I am talking about ..the main problem is that the drywall is about 3/16 and up to a 1/4” thicker then the 1/2 CBU. ( previous homeowner used plaster of Paris to cover wallpaper and used way too much of it in some areas ..making 1/2 drywall almost 11/16 in some areas.) So I am afraid that if I just fill the transition with thinset the transition between the drywall and cbu won’t turn out flush..causing the tile to pop out a little further then the rest in that area. I was also worried if I could get shims behind the cbu how that would affect the tile because it would set the cbu 1/4” out on one side creating a surface hat is out of plane.
Also, the transition is already about 2 1/2” outside the tub ..I was planning on extending it 3”. Lastly, what about the ceiling ..is it necessary to joint the cbu to the ceiling with thinset and mesh tape?

08-08-2019, 06:31 PM
That is not an uncommon problem in tub/shower remodel, Chris, although a bit more pronounced than usual. A photo from further back showing some perspective would be helpful, but my first guess would be that removing the backerboard from that wall, shimming or sistering all the studs in the tub area to allow the backerboard to more closely plane with the wall outside the shower seems the most likely option. If the wall is very uneven, further measures may be necessary at the joint, but that is not usually a major issue.

Or you may elect to leave the walls as is and use some clever profile at that joint to create a "feature" that deals with the problem. I've always been a large fan of features in remodeling work. :)

As to your question about the joint at the top of the shower walls, some codes require that joint to be filled and taped as a fire control measure, but you'd need to verify that locally. In any case, you'll want to verify how flat and level the ceiling is before you proceed with tiling your walls. Not uncommon to find some real surprises there.

My opinion; worth price charged.

08-09-2019, 06:16 AM
Sometimes, Chris, trying to save the existing drywall turns out to be more work than simply tearing it all out and installing new.

Yeah, you could do some things to mitigate the difference but it will be noticeable, I think. Real question is, given all the work you've invested thus far, will YOU be satisfied with it.

Me? I'd be removing that light fixture, the medicine cabinet, and the rest of the drywall on that wall. For $30 and your time you can get the CBU and DW joint even.

08-09-2019, 08:08 AM
I'd seriously consider Dan's advice on this. I think it'll be the same or less work to just replace the sheetrock, and probably turn out looking better in the end.

08-09-2019, 09:36 AM
Hey Chris and Welcome to the forum ..
And welcome to the wonderful world of bath remodels.. where everything can you do right can feel like it leads to another revelation of a previous wrong ;)
I would agree with the Above sentiments; you may well be time ahead by correcting ( removing and replacing) the existing drywall/ plaster. I’ve tried to work around these same issues many times and was always left bitter and frustrated in the end with the many comprises that had to follow.

Back to the Tub surround; I am curious if you are using a membrane over your backer board ? Was the backer board installed with a moisture barrier under it ( over framing )? This can influence the membrane question.

08-09-2019, 10:22 AM
how about set the tile so it overlaps the drywall transition joint. use a plane/chisel to remove some drywall on the surface of the overlap so they are in the same plane without a hump. put a schluter profile there or a pencil trim piece. i think the amount the tile is set into the drywall will not be very noticeable.