I'm putting on 3/4" hardwood flooring over my family room, where the floor is concrete. I nailed in the subfloor using 4'x8' plywood boards. My problem is
that the concrete floor wasn't that leveled and one area where the 4'x8' subfloor boards meet, the don't meet at exactly the same level. This line of discontinuity runs parallel to the direction of the hardwood strips layout. It didn't seem to look like much of a problem but I've now come to this point on my row by row nailing of the hardwood that this 'slight dip down' is making it very difficult to mate the new strip's tongue into the already nailed down strip's groove and nailing the new strip's groove tightly onto the subfloor.