Check the flatness of the subfloor. Use a straight piece of lumber that is between 8 and 10 feet in length to find any areas of the subfloor that aren't level. Simply lay down the plank and look for dips beneath it or raised humps. Mark any problem spots you find. Move the plank across the floor 1 way, then turn it diagonally and go across the surface again.[6] Hardwood Floors
To fix a buckled floorboard, you need to be able to access the floor from below. The way to tackle this problem is to put weight on the buckled area from above — a cement block works well. Then install a 1 1/4-inch screw in the buckled flooring from below. Allow the screw to penetrate only halfway into the flooring, or it may come up through the finished surface. Driving the screw through the subfloor and into the flooring pulls the flooring down against the subfloor and gets rid of the buckled spot. Hardwood Floors