Type of Floor
The first step is to see if you can access the joists and whether they are concealed or exposed. The procedure you use will vary in both cases.
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In case they are concealed, you will need to drill holes on 45 degree angle into floor boards. Then you will need to drive in either cement coated or ring-shank nails. The idea to using these nails is that the smooth nails can get loose and the squeezing issue can comeback after a while. Afterwards, countersink the nails head an eighth of an inch below the surface of the floor. The holes can be filled with wood putty. Once it dries, sand off the excess putty and you will have a smooth finish.
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In case that you have access to the joists, it becomes relatively easy to do the same job. You can watch the movement as someone walks on the floor. If a sub-board moves, you can tighten it with the help of a tapered shim.
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Pull Down Loose Boards
If there is no movement, it indicates that the floor is loose and needs to be nailed down. You can pull down the loose board with the help of an inch and a quarter inch round headed screws. You will need to drill holes and use washers to make sure that the screws do not pull through the sub-floor.
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Strengthening the Bridge
If the bridging between the joists is loose, you can drive in a larger nail at an angle to fix the issue. The squeaking issue should be fixed once the above steps have been done.
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