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sugarhousemama 12-02-2010 03:28 PM

Subfloor and Porcelain tile prep
4 Attachment(s)
My house was built in 1941. That will paobably explain the quandry I'm facing.

We are remodeling and laying new tile in the bathroom, hall, kitchen. The areas all flow together and we are laying the same tile throughout, so it is necessary to have the flooring even in all the rooms.

Currently, it is not. The jokers who remodeled the house before did some pretty wonky things.

We have decided we need to strip the floors down to what we were calling the "subfloor". After spending some time on this forum, I believe I am mis-naming the subfloor.

Attachment 27319

Under the current tile job in the bathroom, there is a layer of morter, 1/4" cement board, and then these wide, diagonal slats. We've been calling the diagonal slats the subfloor. They run throughout the house and are obviously original.

The picture above is the transition between the bathroom and the hall. The hardwood flooring for the hall was installed directly on the diagonal slats. The hardwood hall will be removed and tiled with the same tile for the bathroom and kitchen.

Attachment 27322

This is a picture of the transition from the hall to the kitchen. We have the current tile, a layer of morter, a 1/4" cement board, a 5/8" thick piece of plywood, what appears to be some glue, and another piece of 1/4" thick (probably) particle board all apparently installed on top of the diagonal wood slats.

So my question is this: What do I call those diagonal wood slats? We have to remove everything down to the diagonal slats so we can start with a level surface (since the kitchen, hall, and bathroom, all currently have different heights).

What do I put on top of the diagonal wood slats? I was planning on just putting cement board down and then tiling on top of that - just like what was done in the bathroom. Is that acceptable? Or do I need to put plywood down on top of the wood slats, then cement board, then the tile (similar to what they did in the kitchen, without the particle board).

The ironic thing is that the kitchen - with all that support - has about 1/3 of the current tiles cracked and damaged. i dropped a glass in the kitchen once, and the tile cracked. The glass? Didn't break. Every tile in the bathroom is perfectly fine and I drop my hair dryer or curling iron on a daily basis!

Advice and tips would be greatly appreciated!

Oh - as a side note - I'm not wanting to remove the cabinets in the bathroom or the kitchen. The different floor levels mean that the kitchen cabinets sit about 1 inch higher than the bathroom cabinets. I could put trim around the base to hide any gaps, but that seems like a big difference.

ccarlisle 12-03-2010 06:38 AM

Those diagonal plans are your subfloor - the plywood or CBU that is on top of that in an underlayment.

Concrete Backer Units - or panels - offer a surface that is easily tiled to; they offer no structural support and can cause tiles to crack if not properly installed/supported, so if you are looking for more support, one or two layers of plywood is the way to go. Properly prepared, bonded, screwed, positioned etc - plywood offers more to tile to.

1910NE 12-03-2010 07:57 AM

as stated, the diagonal planking is your subfloor. i wouldn't be surprised if it isn't the same 7/8 thickness that i have in my old house.

when i was tiling the bathroom, i used some boards from my attic to fill in some holes in the subfloor, and made sure the whole thing was secure. then i screwed down 1/2 plywood (make sure you get the kind with at least one "clean" side) over that. finally, i put masonary board over that.

if you have transition issues from room to room, you might be able use varying thickness of plywood to get everything to the same height, but that will be tricky. a simpler option would be to use doorways as transitions. instead of tiling through them, use hardwood.

sugarhousemama 12-03-2010 02:44 PM

So is it generally thought that I should put plywood down over the slats? The current job in the bathroom just has cement board down directly over the slats.

I suppose I would have to tear it all out and inspect the subfloor.

Can I skip the cement board and tile direclty to the plywood? I thought that wasn't recommended. Especially since it's the bathroom and the kitchen....

Thanks! Your thoughts and advice are helpful!

ccarlisle 12-03-2010 06:47 PM

Hopefully more people will state their own preferences but I can tell you what I see as the reasoning behind all this - and that is because, for a floor, you need dimensional stability i.e a stable enough of a base that will not cause tiles to crack, from either top-to-bottom loads, or from side-to-side loads. Plywood provide that and two pieces more than only one. So you will see pros put down two layers of plywood right onto the joists...

Now if you have diagonal planks, then that can act as one of the layers of plywood - almost. Not the best of all worlds - but it would do. So many people put down a 5/8" sheet of plywood over the planks and tile drectly to that. There are a few more things you have to do for a succesful job in this case, but it is do-able...

Now many purists will go one step further and that is they'll put down an 'anti-fracture membrane' on top of the plywood to further prevent any cracks from happening. One product used here is called 'Ditra'. So you have from bottom up: floor joists, diagonal planks, plywood, thinset, Ditra, thinset, tiles.

This is normally done in kichens and bathrooms and where good tiles are expected not to crack. Some people skip all this - and they're people who can live with problem there.

But one thing is frowned upon and that's cement board on the floor. As I said, it does not provide the dimensional stability plywood does, and therefore is unsuitable, IMO, as an underlayment.

Look, I can't tell you what to do in your particular case, with your budget, your taste and your available manpower - but that's the way I see it.

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