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Q. We saw some cork flooring on special and we were considering putting it in all - or part - of the upstairs studio in our barn. Although we used 1 1/8 " plywood for the rough flooring there are some areas of unevenness between sheets (maybe 1/8 inch or so). Should we try to sand down the floor to get it even? If so, what about nail heads? Or, should we put down some leveling material before the flooring (such as thin plywood or OSB or ...)

A. When installing flooring such as cork, the surface needs to be flat. Because the tiles are relatively thin and pliable, they will bend over any dips, bumps or ridges in the underlying surface.

On plywood sub flooring, you should begin by sanding any major problems out. If you really have a difference between sheets of 1/8” this will need to be sanded down. Any nail heads that are at or near the surface can be driven down into the plywood to a depth that will get them out of the way.

Once the major problems are removed, you can then install underlayment. With 1-1/8” sub flooring, this is optional. There is an OSB type product that is about 1/4” thick, or you can use heavier particle board. The thickness of the board used will translate into how much of the inconsistencies in the floor will be telegraphed through to the new surface. Embedding the underlayment in adhesive or leveling compound will remove more of the inconsistency, but will add a great deal of difficulty and expense.

If you do install underlayment, use ring-shank nails that are designed for this. You should nail approximately every 6 inches over the entire sheet. Be sure to consider what adding to the floor will do to stairways that serve the area. All stair risers must be within 3/8” of each other in a run of stairs. If you add 1/2” of underlayment and 1/4” of flooring, and you did not consider this when framing the stairs, you will need to compensate on the stair treads, because you just changed the first (or last) riser in the stair run by 3/4”.

 
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