How to install hardwood on a rough floor

I have been installing hardwood for customers for a few months and things have been going well but seems I met my first challenge. When I installed 4" wide 3/4" thick mahagony flooring there is excessive height difference, maybe upto 1/10 of an inch in rare cases, between adjoining boards.
I investigated and found this is due to the chipboard (3/4" OSB) floor being very rough. Even though there is 1/5" thick plywood on top of the OSB the problem persists. To correct the problem do I sand the OSB floor or smooth it with floor leveling compound? Or is there another solution?
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I have been installing hardwood for customers for a few months and things have been going well but seems I met my first challenge. When I installed 4" wide 3/4" thick mahagony flooring there is excessive height difference, maybe upto 1/10 of an inch in rare cases, between adjoining boards.
I investigated and found this is due to the chipboard (3/4" OSB) floor being very rough. Even though there is 1/5" thick plywood on top of the OSB the problem persists. To correct the problem do I sand the OSB floor or smooth it with floor leveling compound? Or is there another solution?
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use self leveling latex and sand smooth this should take care of most of the problem. The latex is much easier to sand then the osb. I assume most of the flooring is T&G

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When I put down a Pergo floor a few years ago there was a requirement for the floor to be no more than 1/8" (or something like that) out over 6 feet. I had a place or two where there was a valley and used Jif-Set with vinyl sealer to level it. I found it to be not quite as self-leveling as described and used a bull float for additional leveling.
todd
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Also check your floor boards. Flooring expects to be sanded before a finish is put over it and it's not out of the realm of reason that your floor boards are not all even - though yours does sound like quite a difference. If the problems are in the area of OSB joints then it would seem likely that the OSB subfloor is contributing to your problems, but if the problem areas are in the middle of sheets, then I'd look again at just how much the OSB is affecting your flooring. It may not be as the much the OSB as you think. You should easily see a difference of nearly an eighth of an inch as you describe so if you do, I'd certainly lay down some leveler before putting down the 1/5" sheets. BTW - what is 1/5" plywood? Is that an English approximation of a metric measurement?
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Yes, its 5.2mm thick plywood, so that translates into about 1/5". Sold here in Canada.
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I guessed that might be the case. BTW, please include quoted text when making your replies so we can see who and what you are replying to. Snipping is good, but complete snipping is not.
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Bizarre! Could you have some boards upside down? The T&G is not always symmetrical. ALso, the bottom face of the groove edge should be relieved to make the top edges close up more easily. Wilson

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