Bathroom remodel down to the studs and joists

[ChrisO]

I've spent hours reading this forum over the last few days. Thank you for all the great advice everyone has.

My project is a total remodel of the main bath in my house. Right now I am working on the floor.

There used to be badly done vinyl over a patch-work of cement and plywood on top of a 1/2" plywood subfloor. There was obviously water damage several times in the past that for the most part was never repaired but just covered over.

At least half of the plywood subfloor is damaged (separating layers and very soft) so the plan is to cut out nearly all of it.

The hallway outside the bathroom is 3/4" thick hardwood on top of the 1/2" plywood subfloor so I would like to keep the bathroom floor close to that height.

Current plan is to use 1/2" plywood again on top of the joists (so that it matches the height of the old subfloor in the couple areas that would be troublesome to remove) and then screw another 3/4" plywood on top of that.

This already adds up to the height of the hallway floor. I was going to use Ditra after reading about it here to keep the height down a bit but the problem is that the tile I am putting on the floor is 1" hex which is too small for Ditra.

I then found a reference to Durock Tile Membrane which looks like it could be a good solution to use when Ditra won't work.

I tried finding others that have used the Durock membrane on this forum to see how they liked it but couldn't find any information about it.

My questions are:

Has anyone tried the Durock Tile Membrane and would it be a good solution to use under 1" hex and on top of plywood?

And, does 1/2" plus 3/4" plywood sound like an acceptable floor for under tile? Would I be OK with something thinner than the 3/4"?

[Davy]

Hi Chris, I think I would put down the 3/4 first and the 1/2 inch plywood on top of it.

You will have to use something other than Ditra, can't use anything under 2x2's over it.

[bljack]

Are you sure it's 1/2" and not 5/8" plywood? See the ad on the right for Noble products? I don't know about Durock membrane, but Noble CIS is a great product and is only 1/16th ish installed and it doesn't care what size your tile is. Eric (E3) is a regualar here and if you ask him, he might even say that overlaying the 1/2" ply with a second layer of 1/2" with a full spread wood glue to fully laminate the two layers to make a full 1" thick layer might be good to go. Noble sells directly from their site as well as from tile shops so if there is no dealer near you, you can get it from them with $5 flat rate shipping.

[ChrisO]

Thanks for the replies.

I measured in several places and it is 1/2" for the subfloor. The reason I was going to put 1/2" down for the first layer is so that it would be even with the area of existing subfloor that won't be cut out. Then I would put 3/4" (or 1/2" or 5/8" if they would work) on top of the new and old 1/2" subfloor.

I'll check on the Noble product. I was looking at getting their niche for the tub/shower area.

I've been Googling the Durock membrane but haven't found any one that has used it yet. Looks like it is new so not much info out there yet.

[cx]

Chris, you really wanna remove all that half-inch subflooring. Especially since even the good parts are likely not in real good condition.

The very best you can call a half-inch first layer over joists is a spacer.

And you don't sound like you need a spacer.

Cut it all out and start at the joists with a minimum of 3/4" T&G subflooring or square-edge 3/4" with blocking at the seams.

Then, as Davy suggested above, it would be best to add another layer before you tiling substrate and tile.

But you can, technically, install your substrate directly over the single layer of 3/4" subflooring if you want.

My opinion; worth price charged.

[e3]

without knowing the joist spacing,span (deflection) ect., ect, you can in stall CIS over a wood substrate assuming it's solid. You could also go with 3/4" ply and CBU.

[ChrisO]

I'll go ahead and cut out all the old subfloor (shouldn't be too much more work since I was taking out near all of it anyway). I'll use 3/4" T&G for the first layer.

What would be a good second layer plywood thickness? I would prefer thinner to try to keep it as close as possible to the same height as the hall floor but having it more solid is more important.

So there will be 3/4" T&G, second layer plywood (screwed and glued), membrane then tile.

The joists are 2x10 (1.5x9.25). 16" OC with a span of about 12 feet. They look to be in good condition. The Deflecto says I should be good.

Since I'll be cutting out the current subfloor, I was also going to put some 2x10 blocking between the joist around the perimeter (to give the edge some extra support) and also in a few other places spread throughout the span of the joists.

Sound good? I just need a recommendation for a thickness for the second layer of plywood (and what type of glue would be good between the layers).

Thanks for all the quick replies!

[ChrisO]

I have three little kids that sometimes splash the floor while in the bath so I was interested in adding some waterproofing under the tile just in case (another reason for wanting to go with the membrane). If using NobelSeal, would it be better to use the TS rather than CIS?

Also, I will be installing an electric radiant floor mat. Would this get embedded in thinset under the membrane or would it go on top? I know Ditra says under but I'm not sure what the others such as NobelSeal or Durock Membrane recommend.

[cx]

Chris, both the NobleSeal TS and CIS are waterproof membranes. You need to treat the joints between sheets properly if you're using them for that purpose.

The minimum thickness for a second layer of plywood subflooring is 3/8ths-inch. If you elect to use the NobleSeal, you can, per manufacturer's instructions, install it directly over the 3/4" subflooring.

If you elect to do any gluing of the subflooring layers it must be done with a full-spread wood glue. Titebond II is my personal choice for such applications.

I would want any uncoupling or crack suppression system to be on top of any radiant heating system, but you might wanna contact Noble Company for their recommendation (800-878-5788).

My opinion; worth price charged.

[e3]

we really dont care which side we're on HOWEVER Nobleseal does have SOME R-Value .8 and will slow or lower the heat transfer.Installing it below the heat will help by offering SOME insulation value.