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Subfloor thickness


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06-05-10, 12:22 PM   #1  
Subfloor thickness

I am having to replace my top subfloor because it was too much work to prep it for tile as the three layers of linoleum that the previous owners had left was just too much to handle. Anyway when I got to the first layer of subfloor it is 1/2". What would you recommend putting on top of that to make it nice an sturdy for tile? What would the professionals do to get it ready. I am going to be using 12x24" tiles with electric radiant heat below. Thanks.

 
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06-05-10, 08:11 PM   #2  
Thin set is one possibility.

 
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06-05-10, 08:28 PM   #3  
You will get your best answers if you ask this question in the tile forum. But a 1/2" subfloor is right out. You need a floor that's solid with no deflection. I'd recommend adding a minumum of 5/8" subflooring on top (3/4 is better), followed by a layer of cbu. Of course you didn't mention your joist spans or the center spacing of the joists.

Tile guys are pretty particular about their subfloors since they aren't going to stand behind their work if the subfloor isn't up to spec.

 
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06-05-10, 08:56 PM   #4  
3/4 is what I was planning. What is cbu?

 
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06-05-10, 08:59 PM   #5  
How do I get this to the tile forum? Do I just start a new one?

 
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06-06-10, 04:48 AM   #6  
You would start a thread here; Flooring Tile - DoItYourself.com Community Forums

cbu is the same as cement board.


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06-06-10, 05:49 AM   #7  
Can the moderator close this please? Thanks.

 
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06-06-10, 08:54 AM   #8  
Not intending to hijack the thread but I'm a little confused regarding the definition of floor components.

I thought that the subfloor was installed during construction to provide a working surface. In my area it's typically 1/2", spans the floor joists and is laid underneath wall plates. The next layer of floor was called an underlayment and it is typically 3/4" plywood (except when a 3/4" hardwood floor is installed as a finish floor). If the finished floor is carpet, vinyl or tile it is installed over 3/4".

 
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06-06-10, 09:05 AM   #9  
You think you are confused?

 
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06-06-10, 01:59 PM   #10  
Posted By: wendans You think you are confused?
In your case a good rule of thumb for tile support is a minimum of 1 1/4" laid over properly spanned and spaced floor joists.

 
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06-08-10, 06:26 AM   #11  
Wendans

1/2" subfloor won't fly for a ceramic tile installation. I'm assuming the tile you will be using is ceramic. If its natural stone instead, we have to talk some more.

Add minimum 5/8" (3/4" would be better) exterior glue bc plywood over the existing subfloor. Screw it into the joists with deck screws. Screwing into the subfloor won't help much as the screws tend to strip out in plywood that thin. Then install your heating system over that. If your installing heating cables, you'll need to install plastic lath over the entire plywood underlayment first. If your installing heating mats on the whole floor, you can skip the plastic lath. Then use self leveling compound (slc) to cover the heating system. You'll have to use the recommended primer for which ever slc you choose to cover the underlayment, and heating system. Then pour the slc. Read the directions for whatever slc you choose and follow them to a T. Install Schluter Ditra over the slc with good quality unmodified thinset. Then install your tile with the same thinset.

Theres a lot here so ask questions if your not sure.

Perhaps a moderator can move this thread to the tile forum where it belongs.

 
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06-08-10, 04:09 PM   #12  
I have taken all of the old crap off which after looking is what it was. I put down 3/4 (9ply when I counted) beautiful plywood. I told them I wanted the strongest plywood they had. Now, do I need 1/2 on top or is the thinset and ditra I am going to use enough?

Yeah, I guess they could move it if they want to.

 
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06-09-10, 08:53 AM   #13  
I'm not sure where you are going from here. Are you still installing electric heat? What kind of tile are you installing?

 
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06-09-10, 10:17 AM   #14  
Yes, electric radiant 1/8 thick wire. Just wanting to know if people recommend a 1/2 top layer or will the thinset on the wire and then ditra on top of that and then the tile.

The tile is porcelain 12x24 tile that is rectified. We are going with a 1/8 grout line.

 
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06-09-10, 12:58 PM   #15  
If the o/c spacing of your floor joists is 16" you don't need to add another layer of plywood. That being said, more plywood is always a good thing.

 
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06-09-10, 05:26 PM   #16  
But I have had people say that I need at least 1/1/4 or even 1 1/2" subfloor? Will 1/2 make it more stable? What about even 3/8" on top?
From this point I can only go up another 1 3/4" before it starts affecting doors and things and some can't be cut.

 
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06-10-10, 11:05 AM   #17  
You can install ditra over 5/8" t&g plywood subfloor, with no additional plywood added. The 1 1/4" that you have probably heard about is installing ceramic tile directly to plywood (not recommended). For that type install you need 2 layers of plywood. You also need 2 layers of plywood for natural stone. You do not need 2 layers for ceramic if you have the 5/8" ply as I mentioned above and you are on 16" oc joists, but that is bare bones minimum. Adding more plywood is always a good idea.

From this point I can only go up another 1 3/4" before it starts affecting doors and things and some can't be cut.
If you can afford that kind of additional height, then yeah, add more plywood. 1/2" bc exposure 1 plywood is what you want.

Will 1/2 make it more stable?
Yes it will. Adding more plywood will make the floor stiffer, and help big time with deflection between the floor joists. Add more plywood, it'll make you sleep better.

 
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06-10-10, 01:48 PM   #18  
That is what I wanted to hear. 1/2 is better than 3/8 I know. I wish 3/8 would work but I would be better off with 1/2 right?.
How much height would the 1/8 wire plus thinset, plus thinset and then ditra and then thinset and then tile usually add?

 
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