Hi. I want to tile the walls in the shower. I noticed the old drywall is thick with two layers, the top layer is a half an inch gypsum board and the bottom layer is a half an inch compacted paper (sound barrier, I guess). I am replacing the drywall with a half an inch cement board. If I remove both layers, what do I use to compensate for the second layer? Do I need to install two layer drywall, one regular drywall in bottom and the cement board on top?

Thanks for your help.

Amir

You don't need 2 layers. If you are trying to get it to be the same thickness as the rest of the walls, then it's OK to put drywall or anything underneath.

Thanks. I actually managed to remove the top layer (drywall) without too much damage to the bottom compact paper layer. Is it OK to install cement board on the bottom layer?

In order to avoid damaging ceiling, I did not remove the drywall to its entire height (a foot short from ceiling). Rather, I cut the drywall but then in the process, I cut the bottom layer too. Is there a concern about moisture since the bottom layer is cut through its width?

I'm guessing the bottom layer is Homosote which has many uses, (my house was sheathed in it in 1967 and then sided in cedar T-111). Yes, it's OK to install cement board over just about anything, but make sure there's no give in the wall if someone presses on it, and for tiling you want super straight flat corners and all surfaces flat and plumb. I would be concerned about moisture at the top edge and might remove it to the ceiling and put in new drywall if you don't tile all the way up. Score a neat line at the very top of the wall so you don't disturb the ceiling.
Or just go a bit higher with the tile, overlapping the place where you stopped cutting. As long as the old and new align.

I am going to tile it all the way up to ceiling overlapping the old and new drywalls.

The old drywall is painted over several times and is now painted with an oil-based paint. Do I need to peel off all paints or only the top coat?

Hi guys...

I got to say, joypulv, I really disagree with your advice here (sorry)! Build out the studs with drywall? That is never a good idea in a wet area as even cement board is not waterproof and if water gets to the drywall it can only lead to wicking/damage and major issues down the road, for sure.

In my opinion, DO NOT leave homosote or any compressible material under a new cement board installation. If this was my job I would build out the studs using 1/2" plywood or rip some new studs down to 1/2" thickness and secure them to the studs properly. Then I would apply some 15LB felt/tar paper (to the drip edge of the shower) over the built out studs and then I would apply cement board to the studs as usual.

Tape all cement board seams with an alkali-resistant tape and use the same thinset you are setting yout tile in to fill the seams. Use alkali-resistant screws, for best job. Cement board(s) will corrode regular sheetrock screws, so beware of this, OK?

Blending the old with the new a foot below the ceiling should be no issue... just tape and blend the seam correctly... ;)

Finally, consider installing backing for a GRAB RAIL in the shower... safety first, especially in the shower!

Mark

Thank you both for your advices. My next questions are:

Should the lip at the edge of tub be tiled over?
How do I intall a grab bar? Is there a preparation work before I install the cement boards and tiles?

Thanks again.

Hi HM09

The cement board should set just about an 1/8" above the lip of the tub...do not set board directly onto the tub lip as the board can "WICK" water up the wall and slowly destroy the board.

The space between the cement board and the tub should be filled with the tile thinset (from a bag) or you could even use silicone here.

The cement board should come just past that tub "lip" on the tub so that the tile can set onto the cement board WITHOUT coming in contact with the lip.

The tile should not sit on the top of the tub...keep a 1/16" to 1/8" off the tub. When grouting you can grout this joint or if you want you can use a color matched silicone to fill this gap all around the tub.

Finally, for a centered grab bar, use 2"x8" joist material to span two stud bays centered at the height you want your grab bar to be set at. Then, after your tile is grouted and dried you can drill some holes in the tile and mount the grab bar. Use silicone in the screw holes and on the screws when securing the grab bar.

Mark

Hi Mark. Thank you very much. You've been very helpful.

I read on internet to use a ledger on the wall one tile height above the tub (first row of tiles) and use that as a base to level tiles and support them before cement sets in. Is this necessary? If not, what would be the best way to level tiles and to start the first row?

Thanks again,

Amir

Hi Amir...

Yup! The ledger strip on the wall is critical. Set it one inch lower than a whole tile and then after all the tiling on the wall is done you'll remove the ledger strip, silicone the holes left in the wall by the screws that held the ledger strip and measure for the tiles to be cut and install them... ;) If you set the ledger strip one full tile up and the tub is not perfectly level you could end up with a really thick grout line between tub and tile OR you could end up trimming 1/16" off tiles... both of which are a nuisance! Keep the ledger strip one inch lower and you can plan to cut each tile so you end up with a consistent grout line.

Remember to leave that 1/16" to 1/8" gap between the tub and the new tile and grout or caulk after the tiles set.

Mark

Please see next question

Repeated question. Please next question.

What is the right mixture of water/cement to tile the wall and joints between cement boards and the boards and drywall or tub lip? The bag says 1 liter of water for every 4 kg of cement but there seems to be too much water in it as the mixture flows down the wall.

Also, can I cement the tile and fill the joints at once or I should fill the joints first, let it dry and then install the tiles?

Thanks

Amir

You want to mix the thinset to a consistency that will stay on the walls... kinda like peanut butter.

You can embed the tape as you go or you can do it first... up to you. As a beginner, I would recommend that you do it first (seams and corners), but be careful not to build any spots that give you high points in the wall... HARD TO REMOVE AFTER THE FACT, OK?

Mark