Ditra in place of plywood?

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Old 10-05-09, 02:27 PM
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Ditra in place of plywood?

Hello,

I am looking to install some new 12X12 tile in my backhall (approx 65 sq ft). Once all old flooring is removed I will be left with 5/8" Plywood subfloor situated on 2x10 joints spaced at 16" OC.

I know that tile mantra is to have at least 1 1/8" subfloor in place (as I have done in the past) but now see that on their own website Ditra-XL was used over a 3/4" subfloor on 24" OC and that it 'passed cycles 1 through 12, thus achieving a Heavy rating per the TCA Handbook for Ceramic Tile Installation'

Does this seem right or too good to be true? I don't mind spending more for a good product and if it also eliminates another step for more plywood I am all game.

Thanks-
Shaun
 
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Old 10-05-09, 02:47 PM
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Hi Shaun

You don't say what the unsupported span of the joists is. Thats important info.

Is the plywood square edge plywood or tongue and groove. Regular ditra can be installed over 5/8" t&g plywood on 16" o/c joists properly spanned, according to Schluter. Just so you know, that is bare bones minimum. It's not an installation I'm comfortable with, but theres lots of folks that do the testing that are smarter than me. Ditra is a great product. Adding more plywood will make it even better, but its your call.
 
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Old 10-06-09, 08:01 AM
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Thanks for the reply. The unsupported span is 10' and it's square edge plywood. Realizing it was meeting the bare minimum for requirements I wanted to see if moving up to the Ditra-XL would give me better peace of mind over the installation.
 
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Old 10-06-09, 08:21 AM
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Shaun

Your floor joist system is good. Your plywood subfloor is an issue, as you actually don't meet the minimum. The subfloor must be 5/8" t&g, yours is square edge. If you have access from below, you can put 2x blocking between the floor joists at each of the plywood seams, and then screw the edges of the plywood to the blocking from above. This would kinda make your square edge plywood as stiff as t&g at the joints. Short of doing that, you need to add more plywood.

Ditra XL still requires t&g plywood to the best of my knowlege and you don't have that.
 
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Old 10-13-09, 09:55 AM
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Good info - I think I will put down 3/8 plywood and then the DITRA on top of that. I would hate to finish the project only to be worrying about flexing!
 
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Old 10-13-09, 12:37 PM
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Adding the plywood is a good idea. Make sure the existing plywood subfloor is properly fastened to the joists. Add more screws if necessary. Extra screws wont hurt.

The 3/8" plywood should be exposure 1 (exterior glue), cc plugged or better. Make sure you offset the joints of the 3/8" plywood from the joints of the plywood subfloor. The plywood should run perpendicular to the floor joists (same direction as the subfloor). Use screws only, no glue. Use deck screws (not drywall screws) long enough to protrude thru the bottom of the subfloor by approx 1/4" (1 1/4" screws are probably good). Screws should be every 8" in the field and every 6" at the edges. Avoid screwing into the joists as best you can, should be plywood screwed to plywood. Leave a 1/8" gap between plywood sheets, and a 1/4" gap at the perimeter of the room. The floor should be rock solid when you are done.
 
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Old 10-13-09, 11:04 PM
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All excellent info by Johnny above. The only think I would change is the fastener schedule.

With 3/8" I would go no further than 6" in the field and 4" on the edges. Otherwise that ply will bounce.

Jaz
 
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Old 10-14-09, 02:55 PM
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All excellent info by Johnny above. The only think I would change is the fastener schedule.

With 3/8" I would go no further than 6" in the field and 4" on the edges. Otherwise that ply will bounce.

Jaz
Jaz

I have never had a problem with the screw pattern I suggested, certainly not bouncy plywood. I don't lay out any kind of grid for my screw patterns but they are pretty close to what I stated. I suppose a more aggressive screw pattern won't hurt any.
 
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Old 10-17-09, 08:47 PM
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Thanks for everyone's assistance - I look forward to getting started shortly and still find this to be the most helpful DIY site!
 
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