OT: Replace plywood flooring: Perfect tool

Thanks. I was guessing that, but reading particle board.

Bill

LOL, Actually he did say particle board to begin with.

And I cannot answered your question with any authority. I am not sure if you would even use backer board on a floor.

I would say "no", but I wouldn't nail down backer board, at all. It should be screwed every 6", or so. I put thinset between the plywood and backer, too.

To answer your original question, I was told that if the joists are

Replace the subfloor cutout/patch with the same material as the existing subfloor material.

As John mentioned, span to the middle of two existing floor joists with your cutout/patch.

IOW, if your joists are on 16" OC, your replacement piece with ideally be the same material, and 16" in width (from side to side).

It is very common, and actually recommended, to install a cement backer board of some type on top of the subfloor where tile will be laid.

It is OK to do that with an OSB subfloor. Install with fasteners according to manufacturer's recommendation ... they all have that info on their websites.

The "thickness" of that cement board can be different for each room according to:

1. The status and usability of the subfloor (i.e., flatness, etc.)
2. The height needed for a smooth/acceptable transition into the next room, when you add together the thickness of the backer board, the thickness of the thinset/mortar, and the thickness of the tile.

Providing the floor is relatively flat, 1/4" thick backer board is generally sufficient; but 1/2" is most often used as it has more stiffness and will allow an acceptable transition.

Just insure that the sum thickness of the backer board, plus the thinset, plus the tile, will still give you an acceptable transition in height between one room and the next.

Friends, I know this is off-topic but this group has people who know

If you lay tile down on wood, it will fail soon, especially in areas that will be damp/wet like a bathroom. Wood expands and contracts at a much higher rate than tile (yes, tile does, too) and cement. This will eventually break the bond between the thinset and wood. When (not if) water gets through the grout and under the thinset to the wood subfloor, the subfloor with soak up the wood and expand, accelerating the failure.

Back in the day, tilers used to put down tar-paper on the wood subfloor, then poor a thin bed of mortar with chicken-wire as a base for the tile. When done properly, it worked great and lasted decades. Those installation are a real b!t@h to tear out, trust me. :-) Cement board replaced this process for most tilers. The cement soaks in the water that gets under the tile, without expanding.

Schluter-DITRA underlayment is the best of all worlds in my opinion. It can be put down straight on a wood subfloor without raising the overall height of the floor very much, plus it allows for movement in a saggy floor without cracking the tile or mortar base.

Either OSB or plywood of the same thickness as the rest of the sub-floor could be used... but if you have OSB I'd be inclined to make the patch out of it. Same recommendation on the face grain orientation for either. I'd hope it is 3/4" rated but it may be 5/8" or 1/2" rated... you'll have to measure or look for the grade stamps on the old sub-floor (if you can see the bottom of it).

In cases like this I tend to use the biggest patch that will fit (e.g.,

Regarding the backer board, generally that can be screwed down. I use stainless or ceramic coated torx head screws and try to get many of them into joists rather than just the subfloor. Look for "deck screws" in the store.

I fully accept that some folks will think I over do it sometimes but I haven't had any failures to date so I'll keep doing it!

John

Mortar based demolition _always_ results in upcharge in my remodel bids ...

I learned that once and never needed another lesson. :-)

On 07/02/2016 7:55 AM, Michael wrote: ...

...

I fully agree. Ditra is fantastic. I use it under all my installs except for cement backer board. It is pricey, but check online and buy the big rolls if you have future tiling projects that will need it. Tiling over a fresh concrete slab without some form of isolation membrane is asking for future problems.

-BR