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PeteRich 10-26-2007 08:44 AM

Replacing bathroom ceramic floor
I am replacing a 35 year old mosaic tile floor in a small bathroom with new 12x12 ceramic tile. Under the present tile is a 1/4" layer of plywood on top of a 1/2" subfloor. The bathroom floor itself measures 62" x 66" with a bathtub to one side and cabinets to the opposite side. I am assuming the cabints are directly on the subfloor as that was the way the kitchen cabinets were installed in same house.

Should I replace the 1/4 layer of plywood with Ditra on top of the 1/2 inch (Ditra recommends minimum 5/8)?
should put a new 1/4 layer of plywood underneath Ditra?
if I am going to replace the 1/4 plywood is it necessary to use Ditra at all? Why not just install tile over new 1/4 plywood as it is presently?
Are there any better solutions?

What problems could I encounter in removing the 1/4" layer of plywood?

Also what problems should I expect with re-installing the toilet after floor is done?

I hope this isn't too many questions at once.

Thanks in advance.
Pete :confused1:

NateHanson 10-26-2007 12:41 PM

I think you want to tear up the old tile and underlayment (1/4" ply), then lay 1/4" hardibacker or similar underlayment on modified thinset, then lay tile on the hardibacker.

Tile should not be laid on plywood.

PeteRich 10-26-2007 12:54 PM

OK Thanks. I was told that the "new" Ditra by Schluter Systems was better than cement type backerboard so I was wondering if it was OK to put it directly on the 1/2" sub floor. But I was concerned about (A) is the 1/2" sub floor thickness, as opposed to the recommended 5/8" thickness, a problem & (B) Is it wise to put thinset, to which the Ditra would be applied, directly on the subfloor.


NateHanson 10-26-2007 12:55 PM

I'm not up to speed on this ditra membrane stuff. I'll let someone more current answer that question.

JazMan 10-26-2007 03:22 PM

Are you positive that sub is only 1/2"? Half inch ply is NOT suitable in a single layer system, not thick enough. Years ago they used to use 1/2" with 5/8" over it as the system, then in the '70's many builders started using single 3/4". Measure again, if it is 1/2" I bet someone removed the second layer in a previous remod.

If it is 1/2" you will need to install another sheet of 1/2" or thicker ext. grade underlayment. No CDX grade, which is sheathing grade. No 1/4" plywood anywhere, adds little or no strength.

I like and highly recommend Ditra. You use modified thinset to install Ditra to ply and unmodified thinset to install your tiles on Ditra. Do not install tile directly on plywood, especially in damp areas. Might work sometimes, but cement board or Ditra is much better.


PeteRich 10-26-2007 05:00 PM

Thanks for the response & advice.

I am the original owner so I know the floor is original. It was built in 1971, Ontario, Canada.
I went back & measured again & I measure with an engineers caliper 0.76 inches for the complete thickness of the 2 pieces of plywood. I'm not sure exactly what you mean by a single layer system as it is in 2 layers. One layer of 1/2" & one layer of 1/4". Both plywood. Is that still considered a single layer system?

If I use 1/2" on top of the existing 1/2" & then the 1/8" ditra plus the tile (which is 1/8" thicker than the orig) I'm going to have an extra 1/2" total. The floor is already about 1/4" higher than the hardwood in the adjacent hall which brings me to 3/4" step into the bathroom. Plus there's the issue of the extra height with the toilet. How would I deal with that?

Am I being paranoid?

Sorry if I seem difficult. I guess I didn't realize I would have such a problem with what I thought would be a straightforward DIY job.


jproffer 10-26-2007 05:27 PM

By single layer system he means after you take the 1/4" plywood off, you'll have one layer of 1/2 inch plywood, which isn't enough. As far as your height issues, you can get step-down thresholds, or transitional molding. The extra 3/4" with the toilet wouldn't be a big issue. Add another wax ring.....well not "add", replace the one you have with a total of 2 wax rings, don't "add" a second one on top of an old one.

You don't seem difficult, you seem interested in doing the job right the first time....we kinda like that around here:thumbsup:

This is definately a DIY project. Just research, ask questions here (or elsewhere), get the right materials and the right knowledge and you'll do fine.

OH, btw: Don't add a new layer of 1/4" plywood. A 1/2" sheet plus a 1/4" sheet, does not even nearly equal, in strength, a single sheet of 3/4" plywood.

PeteRich 10-26-2007 05:38 PM

Thanks so much for those encouraging words.

I had heard about people using 2 wax rings for the toilet but didn't realize it was so widely accepted.

Thanks to all of you who responded to my questions with such good advice.

Great forum, this!


SoarOnWings 10-02-2008 02:14 AM

What is the difference between CDX and exterior grade plywword for subfloor?
Sorry that I am late to this thread because I just found it by doing a Google search using some subfloor keywords and was lead to this posting thread. I know the original question was a year old and I was trying to post the original commenter JazMan but because I am not allowed to do so yet because I haven't accumulated enough posting points yet. In the original reply JazMan posted on 10-26-2007, 04:22 PM, JazMan said that using exterior grade plywood for the subfloor but no CDX. I know X in CDX means exterior glue and was always referred to the CDX if I don't want the T&G plywood for subfloor at places such as Home Depot or Lowes. So what is the difference between CDX plywood and the "Exterior Grade" plywood? Why the former can not be used for subfloors? Thanks.


PeteRich 10-06-2008 02:53 PM

Hi Jeff, Thanks for jogging this thread. I lost all my PC stuff a while ago & didn't know how to get back here.

I don't know the difference between CDX & Exterior grade. I couldn't find anyone up here in Canada that knows what CDX grade is.

Just for the record I finally finished the bathroom tiling kob. I ripped up the 1/4" plywood along with the mosiac tiles (It definitely was 1/4") I replaced it with 1/2" exterior grade. I then put Ditra on top using fortified thinset. So now I have 2 layers of 1/2" plywood and a 1/8" layer of Ditra. I then used unmodified thinset to adhere the tile to the Ditra. Everything went smoothly (more or less).

Thanks to everyone who responded with so much help.

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