Underlayment Bath Floor

Old 01-04-03, 01:28 AM
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Question Underlayment Bath Floor

I plan on laying ceramic tile in my upstairs bathroom. I've ripped out the vinyl flooring and found particle board underneath. Will I need to remove the particle board and replace it with better grade plywood before I lay down the cement backer board?

Also is there any way that I could keep the adjoining carpet (from the hallway) level with the finished ceramic tile?

Old 01-04-03, 02:20 PM
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Particle board is never a good backing for tile. Change to good quality plywood, and since this is a bath, cement board over the plywood.
Old 01-04-03, 06:59 PM
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Make sure you're not saying particle board when you have OSB. Many people mistake OSB (looks like flakes of wood) for particle board (looks like sawdust). If you have OSB, you can put the cement board over it and proceed with the tiling.

I find that carpet with a typical pad is usually a compatible height for tile on cement board. You can often just tuck the carpet against the tile with no transition.
Old 01-04-03, 08:23 PM
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Thanks for the tips. I suspect it is OSB and not particle board. However, I have notice that some of this OSB board is damaged from leaking water from the tub. As a result, it seems that I should replace at least part of this board. Since I have 3/4" plywood under the OSB, could I get away with just using a 1/2" cement board over the plywood? This seems like this would give me 1.25" of underlayment. Am I on the right track?


Old 01-05-03, 05:35 AM
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The OSB is adding strength to the floor. You don't want any movement and cement board doesn't add strength to the subfloor to resist deflection. If you feel the floor has no movement when you remove the OSB, then by all means, install the CBU over the primary subfloor.

If the OSB is damage, get it out of there.
Old 01-05-03, 11:16 AM
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Thanks to all of the previous responders.

So I've now ripped out the 1/2" OSB board due to water damage from around the tub. It appears the water was getting under the floor where the previos vinyl met the tub.

Anyhow...before I lay down the Cement board I want to make sure that I don't need an additional piece of wood over the existing 3/4" plywood. The floors seems to have very little deflection. As a result, I'd prefer to just put the 1/2" cement board down. As I've read most of the other messages regarding underlayment, it appears that most experts recommend 1 1/4 " of underlayment and at a min. 1 1/8". I'm a little confused as to what is included in these measurements. Does the Cement board count towards this goal of 1 1/4" underlayment??

Thanks for your help!

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