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Old 02-01-2010, 12:12 PM   #1
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Bathroom Subfloor construction


I have been reading and reading and seem to get only parts of the story and it is getting difficult to see what is right. I am ripping out an old 2nd floor bathroom, some of the subfloor has water damage. I have already torn out all of the fixtures and will be tearing out the sublfoor and moving a wall out a few feet. The plumbing will be relocated by a plumber. The finished dimensions of the room will be approximately 9' x 15 1/2'. I will be placing a large shower and a corner jacuzzi tub (60"x60"). Floor joists are 16" OC and are 2"x10".
I plan to use ceramic, stone or porcelain tile for the floors.
Oh and I'd like to do this "right" as best as I can.

Now the questions.
1. How do I build my subfloor in preparation for the cement backer board.
2. How thick should the backer board be for the floor? 1/2" or 1/4"?
3. Does anyone have any recommendation as to the backer board? The newer, lighter glass fiber facing materials or the cement backer like Durock, permabase, etc...?

Thanks much for all of the experts help!

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Old 02-01-2010, 12:35 PM   #2
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Bathroom Subfloor construction


I like to use 3/4 tongue and groove for the sub floor ( You can use thicker). I also use 1/2 thick cement board on the floor and 1/4 inch on the walls.

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Old 02-01-2010, 07:50 PM   #3
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Bathroom Subfloor construction


1. How do I build my subfloor in preparation for the cement backer board.
Put down 3/4" T&G plywood

2. How thick should the backer board be for the floor? 1/2" or 1/4"?
Backer board on the floor or walls? Walls 1/2". For the floor that is up to you depending on what height you need it to be to meet the other floor heights. Personally I would use the Ditra waterproofing system instead of backer on the floor. It allows for good adhesion, and if your grout fails over time or cracks and the tub overflows it will protect against that

3. Does anyone have any recommendation as to the backer board? The newer, lighter glass fiber facing materials or the cement backer like Durock, permabase, etc...?

Personally I dont like the lighter backer board and I would use Durarock or some other type of other cement board.
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Old 02-02-2010, 07:21 AM   #4
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Bathroom Subfloor construction


So in several places on the web I have seen reference to a bathroom subfloor having to be 1 1/8" high, from what I gather from the replies here that height would be INCLUDING the tile backer? 3/4" ply + 1/2" backer is about 1 1/4"?? (Like my math?

As for the walls throughout the bathroom (not including in the shower), is greenboard still being used? Do I apply a vapor barrier throughout the rest of the bathroom? Do I apply 1/4" backer over greenboard or regular drywall for those areas where I am tiling walls? I will probably tile some of the walls behind the corner tub, but the rest of the walls will just be paint (possibly with just a row of decorative tile)

As for the Ditra...Am I still good with only 3/4" T&G ply? Or do I need another layer of ply above that before the Ditra? Besides height matching, has anyone found any other benefit to the Ditra XL?

Thanks!

Last edited by eemc2; 02-02-2010 at 07:26 AM.
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Old 02-02-2010, 12:34 PM   #5
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Bathroom Subfloor construction


reference to a bathroom subfloor having to be 1 1/8" high, from what I gather from the replies here that height would be INCLUDING the tile backer? 3/4" ply + 1/2" backer is about 1 1/4"?? (Like my math?
I have never heard this before, it can be any height you want.


As for the walls throughout the bathroom (not including in the shower), is greenboard still being used? Do I apply a vapor barrier throughout the rest of the bathroom? Do I apply 1/4" backer over greenboard or regular drywall for those areas where I am tiling walls? I will probably tile some of the walls behind the corner tub, but the rest of the walls will just be paint (possibly with just a row of decorative tile)
GP makes a new product that has a fiberglass face so it wont grow any mold I would suggest you use that. Vapor barrier under all layers or drywall and durarock yes. Dont put any drywall under the durarock. Install 1/2" durarock directly to the studs, install your waterproofing system.


As for the Ditra...Am I still good with only 3/4" T&G ply? Or do I need another layer of ply above that before the Ditra? Besides height matching, has anyone found any other benefit to the Ditra XL?
Yes 3/4" T&G is fine with just the ditra. No tile goes right on the Ditra.


Thanks
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Old 02-02-2010, 02:25 PM   #6
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Bathroom Subfloor construction


My quick searching indicates that it looks like 3/4" T&G ply is pretty easy to find, although it doesn't look like exterior grade, is this ok?

As for a second layer I can't find anything thinner than the 3/4" that is T&G'd, is non-T&G'd sufficient for that second layer?

I can't really find exterior grade that is rated C or better for either layer, most exterior I have found is usually CDX or marine grade. I don't need marine grade for the bath subfloor do I?
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Old 02-02-2010, 02:33 PM   #7
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Bathroom Subfloor construction


I personally use pressure-treated plywood and lumber only in any room with water (baths, kitchen, utility, etc.)
It isn't a matter of IF it ever gets soaked from a leak, but WHEN. You will find it money well spent.
Just MHO.
Mike
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Old 02-02-2010, 04:19 PM   #8
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Bathroom Subfloor construction


My suggestion is to use 3/4" T&G for just over the floor joists. Then install the ditra system on top of that. No need for a second layer bud. If you have ditra you dont need marine grade or other.
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Old 02-02-2010, 04:36 PM   #9
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Bathroom Subfloor construction


Quote:
Originally Posted by wnabcptrNH View Post
My suggestion is to use 3/4" T&G for just over the floor joists. Then install the ditra system on top of that. No need for a second layer bud. If you have ditra you dont need marine grade or other.
Yep

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