Using Ditra in my kitchen [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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05-12-2006, 08:06 PM
Folks: This is my first post. Like some others on this site, I have completed some tile jobs with success on concrete but have not layed it on plywood. I e-mailed John Bridge and he suggested I check out this forum. Very impressive! What I told John was that I had two layers of 1/4" plywood on top of a 3/4" tongue and groove solid wood (spruce,fir??) base floor. The house is 40 years old and I believe that the second layer of plywood was laid over the original subfloor in order to lay a new linoleum floor. I pulled up the old linoleum and plan to use Ditra and then tile. John suspects that the subfloor may be luan which may not be suitable for tile as a subfloor. The first question is I'm not sure what luan is. I'm pretty sure that the subfloor is made of mahogany. Is this luan? Also, does it sound like I could have problems with this application? The framework is 2x10 floor joists at 16" centers at a 12' span. Thanks for any help. Ecurb

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05-12-2006, 08:45 PM
Hi ecurb ... welcome to John's forum.

Over the years vinyl installers have used poplar, mahogany and a very hard pressboard material as their underlayments (usually about 1/4" thick) .... none are suitable in a ceramic tile system. The easiest way to remove these layers is to cut strips in the layers 1 or 2 feet wide using a circular saw with the blade adjusted to the thickness of the material you want to remove. They should peel up a bit easier this way.

Ditra is an excellent product but it won't strengthen the floor, so check to make sure everything is solid and without bounce.

05-12-2006, 09:39 PM
First, you'll have to remove both layer of 1/4" material. As Harry said, there's no wood product of that thickness that should be under ceramic tile. Then, you'll need to screw the 3/4" boards to the joists to secure them. Over that, you'll need to add a new layer of plywood, grade C-C or better, screwing it into the boards, but not the joists. Over that you can install the Ditra.

Here's Schluter System's Ditra Handbook ( See page 8 for your particular floor (structural planks), page 23 for details on installing the plywood, and page 24 for installing the Ditra.

And one more thing. We should make sure that the joists under your floor are stiff enough for tile installation. Can you provide the thickness, height and spacing of the joists along with their span (maximum distance between supports under the joists)?

05-12-2006, 10:07 PM
Thanks for the responses. I'm glad I started looking into this more closely before I started setting tile. I've already bought the tile and Ditra. I haven't bought any thinset yet. I pulled off the pages from the Ditra handbook that you suggested. Looks like I'm going to try ripping up both subfloors and putting down 1/2" plywood. Oh well, it's only more work. Better now than later. The floor seems pretty solid but I want to make sure it's done right the first time. Harry, I see you're from Ontario. I'm from southern Ontario myself. What kind of thinset do you suggest and where to get it?

05-12-2006, 10:27 PM
Tilemaster in Newmarket / Aroura has all the thinsets you need and will advise you which ones are needed for the Ditra.
Use a modified thinset mortar to install the Ditra, use an unmodified mortar to install your tile over the Ditra.
If you're not close enough to Newmarket ... Home Depot has a line of mortars.

05-13-2006, 04:40 AM
Does he really need that much ply going over a tongue and groove subfloor?

05-13-2006, 06:54 AM
Skeeter --

maximum spacing of joists is 24" (610 mm) o.c.
double layer wood floor consisting of:
minimum structural plank subfloor thickness 3/4" (19 mm)
minimum underlayment thickness 15/32", 1/2" nom. (13 mm)

05-13-2006, 08:30 AM
OK, I misread your post, I thought you were saying he needed two layers of ply on top of the t&g. :shrug: guess I gotta learn Board doesn't refer to plywood.

John Bridge
05-13-2006, 10:46 AM
Hi Ecurb, Glad ya made it. :)

05-13-2006, 06:15 PM
Thanks John: I just sat down now with a beer. Just finished ripping up the two subfloors and three layers of linoleum. I'm glad I looked into this as I can see now how I would have run into problems. I'm down to the tongue and groove and will screw it down to the joists tomorrow. Hopefully then, I'll pick up some plywood and get it down so I'll be ready for the Ditra. I was thinking of going 5/8" just to be sure. Do you guys think that's overkill? How should I space the screws? This is awesome to have such a wealth of experience at my fingertips. :yipee: