Mark's Half Bath

[Markg1]

I'm starting another bathroom remodel. This one is a half bath. The room is 5' x 8' with just a toilet and a vanity. The old floor was the thin (3/8"?) Bruce oak. I ripped that up and found 1/2 particle board over 3/4 OSB (except for a 3/4" plywood patch under the toilet). Both the particle board and plywood around the toilet were soaked through and sagging. I cut a decent margin around there and put in a new piece of 3/4 OSB, getting out to get the tongue where I could. Glued and screwed it down and screwed down the rest so it is solid now. I plan on putting down Ditra then a mosaic. The issue is that we want the floor to be about 1/2" higher.

1. I know it doesn't add a lot of strength, but is there anything wrong with putting down another layer of 1/2" plywood or OSB?
2. Should it be glued or just screwed down?
3. I remember reading somewhere that the second layer should not be screwed to the joists, is that right?

[Richard Tunison]

If you need the extra height why not use 1/2in. cement board. Be aware that mosaics smaller than 2 in. are not to be used with Ditra.

[Markg1]

The mosaic is white 2 X1" rectangles surrounding a blue 1x1" square pattern. I plan on filling the ditra with thinset to flatten it out prior to setting the tiles.

[cx]

Mark, it matters not when you fill the Ditra waffles, the manufacturer still recommends against any tiles smaller than 2x2 inches in size.

An additional layer of half-inch subflooring, properly installed, would substantially stiffen your subfloor, especially the part cut up with patches. Use mechanical fasteners only and do not fasten into the joists.

My opinion; worth price charged.

[Markg1]

What would be best to put the tile on then? Cement board, plywood, OSB?

[cx]

A CBU or sheet membrane over the added plywood would work.

My opinion; worth price charged.

[Markg1]

We only want another 1/2", so would 1/4 in plywood then 1/4 " CBU work?

Or would 1/2" CBU be better?

[Markg1]

bump

[Richard Tunison]

Like CX said, 1/2in. ply and a thin sheet membrane will be optimum.
Ditra and Nobel seal are about 1/8in. thick. Greenskin is about at thick as a dollar bill. Many others to choose from.

[cx]

I think NobleSeal measures only about thirty mils in thickness, Richard.

[Richard Tunison]

You are right CX. I stand corrected and will store that tid bit away.

[Markg1]

OK, I hadn't heard of those, but they are kind of like Kerdi, no?

I had just bought a roll of Ditra for that bathroom. Guess I will save it for the kitchen or masterbath where we'll be using bigger tiles.

[Richard Tunison]

Oppps. I forgot about your small tiles when I mentioned Ditra.

Greenskin is peel and stick.

http://www.devcomtape.com/uploads/GS...data-sheet.pdf

[Markg1]

Not finding anywhere I can get my hands on greenskin or Noble Seal by this weekend. Could probably deal with the height of a 1/2" ply plus 1/4" CBU (will be trying to match that to the travertine in the kitchen when we get around to doing that).

Will the 1/4 CBU be good enough water proofing for around the toilet?
Do I need to seal it or is mesh tape and thinset good enough for the seams?

[Richard Tunison]

CBU is not waterproof,,,,,,it just provides a proper substrate for the tile.

Yes, imbed alkali resistant mesh into thinset on all of the seams. Leave a small gap at the perimeter of the room and put nothing there. This is for expansion.