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Tuco 07-22-2007 08:53 AM

Hardiboard and OSB
We are putting tile in our bathroom. We just removed the OSB particle board from our bathroom floor. We have several questions.

(1) We could not remove all of it, there is a 2 inch strip along two walls and the tub. It is one half inch thick. The thickest Hardiboard is about 3/8 inch thick. We are looking for ideas on how to increase the thickness so that the butt joint is smooth/flush. We were thinking of using 1/8th inch thick press board. We would tack the press board down with a few small nails. Then install the cement board with 1.5 inch stainless or galv. screws. Does this sound okay?

(2) If the combo of the press board (or other) and hardiboard still dont exaclty match the existing OSB, is there some plaster type stuff that we can use to level it? What should we use to fill in cracks, waterproof, smooth out joints?

(3) How far apart/ how many screws for installing cement board?

Tuco 07-22-2007 05:09 PM

Thanks for the info! I like the idea of using the thinset. It sounds like I can apply it at an appropriate thickness to make things flush.

Tuco 07-23-2007 05:07 PM

We decided another way to handle this would be to lay some plywood down the same thickness as the osb and then lay the hardiboard on top of this. This would mean the overall floor thickness will be 1/2 inch higher. It seems that in the future one could remove the flooring easier with this setup.

Is this pretty normal procedure? We are a bit concerned that the carpet in the hallway will be considerably lower (3/4 inch?) than the tile in the bathroom. Would this be an acceptable transition? Worried about tripping issues.

Tuco 07-23-2007 07:43 PM

How do I use a sawsall without cutting all the way thru the main 1 inch ply floor? I have a hand backsaw, maybe that would be better?

Also, after doing more measuring, it looks like the carpet and the tile would be at about the same height if we put a 1/2 inch subfloor (butted against the 2 inch strip of osb) and then the hardiboard and then the tile. This figuring 1/2 inch for the hardiboard and thinset, and 1/2 inch for the morter and tile.

Tuco 07-23-2007 08:57 PM

Thanks for the suggestions. Not too new to power tools, but most of the work I do is with metal. If we decide to remove that strip of osb I think I will work it out with a backsaw and chisel.

Anyway, the carpeting with pad measures about 1 inch thick and sits on top of the same OSB that is around the edges of my bathroom. Am I incorrect that the thinset + cement board + morter + tile = 1 inch? The hardiboard that I looked at was 3/8th inch thick. I didnt measure the ceramic tile, but it looks like its also about 3/8th thick. With the thinset and morter, this would be about 1inch and would put the top of the tile pretty close, but maybe a hair higher than the carpet. Could we also use the thiner cement board in case we want the tile a little lower or must tile go over at least 1/2 inch hardiboard?

The flooring in the house is 1.125 inch tongue/groove ply on top of joists. Then there is 1/2 inch osb on top of this. Finally carpet with pad on top of the osb. The bathroom originally had half carpet and half linoleum. We have ripped all this up and cut most of the osb out.

Square Eye 07-24-2007 07:01 PM

To cut doorjambs, I use a back saw. I cut a block to match the height from the floor and I lay the saw on the block. I simply slide the saw back and forth on top of the block to get a near perfect cut every time. You will have to change positions as you cut the casings and the jambs, but that should be no problem after you get through the jambs.

Rustedbird 07-26-2007 03:22 AM

I like to put a raised threshold (not much) just to make sure the water stays in the bathroom. Just thinking that wet OSB and carpet padding might be nice to prevent.

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