concrete backer board over fire block dry wall
#1
02-20-13, 10:12 AM
concrete backer board over fire block dry wall
installing tiled shower in my condo. One wall of the shower is the wall between my unit and the neighboring one. It was covered with 2 layers of 5/8 regular sheetrock. Fiberglass insulation fills the space between the studs with a paper backing on the outside. This insulation is for noise not heat. What is the correct way to layer the wall? Is it one layer 5/8 drywall, felt overlapping the shower pan membrane at the base then the 1/2 concrete backer board and then the tile? Or some other combination of layers? Thanks
Last edited by pgs007438; 02-20-13 at 10:42 AM.
#2
02-20-13, 11:56 AM
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I wouldnt put any sheetrock back in there, just cement board.
The way the last inspector had me do it was;
Note: This is from bare walls / studs
1. Install window flashing (rubber roll about 12" wide) at the very bottom of the wall overlapping into the tub a few inches.
2. Install Tar paper overlapping the flashing, then up to the ceiling.
3. Install Cement board, use multiple layers if you need to build out and use the correct screws
4. Seal cement board joints with joint mesh and mortar
5. Install tiles or whatever you use after that.
6. Cut excess flashing at bottom
7. Seal tiles / grout
The way the last inspector had me do it was;
Note: This is from bare walls / studs
1. Install window flashing (rubber roll about 12" wide) at the very bottom of the wall overlapping into the tub a few inches.
2. Install Tar paper overlapping the flashing, then up to the ceiling.
3. Install Cement board, use multiple layers if you need to build out and use the correct screws
4. Seal cement board joints with joint mesh and mortar
5. Install tiles or whatever you use after that.
6. Cut excess flashing at bottom
7. Seal tiles / grout
#3
02-20-13, 02:08 PM
Whenever there are 2 layers of firerock, it's because the local jurisdiction requires it. It's installed so the seams overlap. You could probably do the same with cement board but you need to find out how the code handles that wall. If the permit office can't tell you, the inspector can - talk to him ahead of time, it will save you from headaches later 
btw - welcome to the forums!
btw - welcome to the forums!
#4
02-20-13, 02:23 PM
Group Moderator
Ditto what Mark said - 5/8" rock isn't all that common on walls, either; 1/2" is the norm so I'd be willing to bet some cash this is a code issue as well.
#5
02-20-13, 02:32 PM
Mitch, common walls in apt/condo's always have 5/8" firerock. Some jurisdictions require it to be 2 layers thick with the seams offset. The firerock will also be installed in the attic between units. Many also require it on garage/house walls. Locally we only have to install 1 layer of firerock in condos and none at the garage/house wall..... it all depends on the local regs.
#6
02-20-13, 02:42 PM
Group Moderator
I stand (sit) corrected. That said, the double layer does still sound code, we're subject to that on the ceilings in the garages of all of our units.
#7
02-20-13, 03:34 PM
You don't need all that flashing and tar paper. what you should use is a 6 mil vapor barrier tacked up on your studs, allowing it lay into the tub part. Then install the cbu on the wall, sealing the seams with concrete tolerant mesh tape and thinset. Now, as far as code goes, on double walling, you will need to get their blessing, but the last time I tried to catch cbu on fire...........
Once you have the cbu set on the lip of the tub, you can tile over it all allowing the tile to finish the fall to the tub rim, cutting the vapor barrier at that point.
Once you have the cbu set on the lip of the tub, you can tile over it all allowing the tile to finish the fall to the tub rim, cutting the vapor barrier at that point.
