New Bathroom remodel

[Keithett]

I'm in the planning stages of a complete bathroom remodel and would like to replace the existing carpet and linoleum with tile. This is an upstairs floor consisting of 2X10 joints at 16" on center. The existing floor is 3/4" plywood, 1/2" sound board then 1/2" strand board.

I was planning on removing the 1/2" sound board and 1/2" strand board then replacing it with 1/2" exterior plywood and 1/4" wonder board. This would leave me room for my tile, thin set and under floor heating while maintaining a finish floor height close to the adjacent room. Does this sound like the correct way to go? I've been searching the internet but keep getting conflicting answers.

Thanks.

[cx]

Welcome, Keith.

Yes, sounds good if you know the unsupported span of your floor joists and they meet the required L/360 deflection requirement and you install your second layer of plywood properly with the strength axis perpendicular to the joists and fasten it only to the first layer.

My opinion; worth price charged.

[Keithett]

Thanks for the quick reply... My span is 10' and when I use Deflecto to calculate the deflection, it says it easily works. I was planning on gluing and nailing the new plywood to the existing plywood so it would act as one piece. The orientation of the strong axis and not nailing into the joist is good advice and something I hadn't thought about.

[cx]

I am a large proponent of gluing all parts of a subfloor structure, but gluing the subflooring panel layers must be done using a full spread of wood glue and a proper fastener schedule. You can't use any gun applied constructive adhesive for that operation.

Here's a good article about installing that second layer of plywood. Much of it may not apply to a small bathroom floor, but I would suggest you follow their recommendations to the extent that they apply. They do not recommend gluing the subflooring layers, but that's actually only because they fear you won't do it correctly.

My opinion; worth price charged.

[Keithett]

I have one other question concerning my tile project.

Am I better off following my original plan by replacing the existing sound board and strand board with 1/2" exterior plywood and 1/4" wonder board or would it be better to replace this with 3/4" plywood then use Schluter Ditra membrane on top of the plywood?

Schluter Ditra would give me the benefit of a waterproofing over the entire bathroom floor.

[bbcamp]

3/4" plywood will make your subfloor much stiffer than 1/2" plywood and backerboard. Otherwise, if both methods were installed properly, either would give you a long lasting tile installation.

[Keithett]

I'm setting large format tile (12"x24") over Ditra in my bathroom. Does anyone have a recommendation on what grout I can use for this? Schluter recommends using a non-modified grout but I'm having problems finding a non-modified grout that will work. I'm planning on using a 1/2" x 1/2" trowel then back butter the tile.

[Keithett]

Sorry, I just realized I said I was looking for grout where I should have said mortar... What I'm looking for is a good quality mortar that I can use with Ditra.

[cwilde72]

Ditraset and Laticrete 317 are my go-to unmodified's.

[Lump]

I second the Ditra Set

[Keithett]

I've been calling around and Ditra Set is not sold by anyone in my area. I live in near Portland, Oregon.

I talked to the people at Laticrete and they don't recommend using Laticrete 317 for anything over a 1/4" thick bed. I see that HD sells CustomBlend but I've read in other threads that CustomBlend is not recommended with Ditra. Finding a good quality mortar for use under large format tile seems to be a problem. Any other suggestions?

[Keithett]

Maybe I'm over thinking this... I've already used Laticrete 317 to install the Kerdi and was planning on using it also to install the Ditra over SLC. Since my tile are very straight with little or no cupping, maybe I can just use a 1/4" x 3/8" trowel and back butter each tile. This would meet the Laticrete 317 requirements. Does this sound reasonable?

[Houston Remodeler]

With an experienced hand that will work.