Bathroom flooring

I am renovating a bathroom. The rooms is stripped to the studs with a plywood base.
I plan to put a layer of cement board down over the plywood as a base for the tilers to work on.
The plywood is rather uneven so the cement board will ride over ridges.
Is there some kind of compound I should apply first to level out the floor before the cement board or should I simply not be concerned?
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snipped-for-privacy@yahoo.com wrote:

how uneven?? Use hardy board not cement board.Hardy board is much easier to work with and also use the screws they recommend.
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wrote:

You could "laminate" the cement board to the floor with thin set. It should level out the ridges and also should serve to make the whole floor stronger.
JK
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wrote:

The 'compound' you need is called a sander, either a belt sander or (easier) random orbit sander. Given a typical 8 x 10 bathroom you can get all the bumps out of the floor in about 15 minutes. Some pros then coat the plywood with the cheapest polyurethane they can find to get better adhesion/performance out of the thinset or whatever they use under the tile substrate board. This method will yield the sturdiest floor for unusually thin or even fragile tiles.. HTH
Joe
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