Is it bad to use mortar to level a floor?


Old 01-27-07, 04:28 PM
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Is it bad to use mortar to level a floor?

We are about to put down the backerboard in our bathroom so that we can eventually put the new tile on top of that, however our floors are not completely level.

The floor height varies +/- 1/8" (1/4 at the extremes). We know we need to level the floor below placing the backer board on it, because the last thing we want is for the backerboard to flex and ultimately cause cracks.

Would it be bad to just use normal mortar to level out the floor (the same mortar we were going to use to afix the backer to the floor before screwing it in? We'd like to just use mortar if possible, and have the mortar slightly 'deeper' in some areas.

We do have some 'self leveling' compoud, but to be honest.. it makes us nervous. We're afraid that since it's so liquidy, that it will find a crack somewhere and run down under the floor and onto the ceiling downstairs.


* Also, is there a 'max' depth for the mortar?
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Old 01-27-07, 04:42 PM
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Whatever backer board you're using needs thinset under it to bed it. The thinset is not there to glue the board down, it's there to bed it and eliminate any voids between the board and the sub floor. The instruction label on the board, if you're using concrete board, will give you instructions that say to do this. Do not skip this step. The tile will come apart if you do. Once the board is properly installed, do your leveling on top of it. Check again when you've finished the board. You may find a lot of it has been corrected or you may not. If it isn't too bad, you can do a little leveling with thinset as you go. If it's still too much when the board is down, self leveling compounds work well.
Old 01-27-07, 05:08 PM
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I did not know about having to use thinset beneath the backer board. I will keep that in mind for my own stuff. Thanks, Smokey. I was going to comment that I thought 1/8" - 1/4" was hardly worth worrying about. When you apply thinset, you put it a little thicker in the low spots for small deviations like this.
Old 01-27-07, 09:41 PM
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Jeff, The main problem with trying to level the backer board with the bedding material is, the fasteners may not be able to reach the wood underneath and won't be able to do their job. I agree that the amount of deflection seems minor which is why I suggested checking the level or flatness again after the board is bedded and fastened. The fasteners put pressure on the surface of the board and cause the thinset to squish into low areas and out of high areas as you work along. Consequently, although you aren't technically leveling the floor with the bedding material, it does tend to have a certain amount of that effect. With such a small amount of deflection, it's conceivable that some of it will be solved during the bedding process. The rest, as you pointed out, should be fairly easy to solve while setting the tiles.

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