In most cases the three wood floor members (the joist, subfloor and finished hardwood) have separated, and the nails binding them are moving in the nail holes. A little dust in these nail shafts makes the boards squeak. That's why talc, wax and graphite offer a temporary solution. But why not try a permanent fix? Oh, by the way, simply resanding and finishing a squeaky floor will do little to solve the squeaking problem, don't let any contractor con you into just doing that.
This separation is generally caused by seasonal shifting of the boards, and you would be well advised to keep the indoor relative humidity levels to about 40-60%. And I do mean all year round. Sadly though some hardwood floors were poorly nailed in the first place. A lot of wood floor contractors will not do the proper preparation of the subfloor, or they will lay a hardwood floor in the wrong direction. Be sure to read my Wrong Way Floor article (free) in the Case in Point section of this web site. Or worse yet they will have stapled the floor down with those awful flooring staples. Read the other free article about these lousy fasteners in the Primatech article in the Floored News. In the worst case you may have a OSB subfloor that got rained on during construction, and now causes no end of popping or squeaking.
I spare no details in this article. I will discuss a simple renailing of the loose boards on up to how to remove and reinstall a wood floor. I will give you not only the methods, but the access to the proper (yet inexpensive) tools to do the job well the first time.
If you can access the floor from under the joists you can try a nifty new product called Squeak-Ender at:http://www.squeakender.com
They have several well-engineered solutions to squeaking and sagging floors, and its worth checking out. These products will save you from having to nail the floor from the top. The Squeakender's web site has excellent illustrations of these products, so I needn't explain this method further. Suffice it to say these are brackets that are fastened to the joist and subfloor, and then are ratcheted down to bring the subfloor permanently tight with the joist. Oh how I love good engineering!
You may however, have to use some of the following methods if these Squeak Ender products are only somewhat effective. Or you are a dedicated DIYer and hate to buy anything you think is that expensive, complex or worse yet "engineered". Also, what do you do when you find that the second floor boards squeak or a finished basement ceiling covers the underside of the floor joists on a main floor? Just how can you re-nail a hardwood floor in these situations?
Well, you will need to find where the joists run under the subfloor, so that when you re-nail the hardwood, it will pull all three flooring members together down and stop the movement. This method as you can imagine works best when the hardwood boards run at right angles to the joist.
To find these joists, remove the quarter round or molding from the edge of the floor. You only need to remove the molding running at right angles to the joist. Drill a 1/4" hole in this space (or no larger than the molding will cover) and insert a bent coat hanger or stiff wire. In either direction you will feel the wire bump up against the joist. Measure over and drill another hole closer to the joist and test again, until you have determined the edge and then infer the center of this joist. Its easy to mistake a cross brace for a joist so always double confirm, by pre drilling or "nail spinning" a finishing nail into where you think the joist is.
When you hammer a nail into the joist it will feel firm all the way down if you have located the center of the floor joist. I explain nail spinning later.
Do the same on the opposite side of the room, and snap a chalk line between the two. This should represent the run of the floor joists under the hardwood strips. They should, in most modern houses, run every 16", but you may have to drill more edge holes to confirm this. If the room is wider than 15 feet, there may be a supporting beam separating two separate runs of joists. And they may not line up with each other across the room. Also, around stairwells the floor joists may run a little closer, and be framed in differently to accommodate a joist header. You can only see this from below, even if you have to poke a small view hole in a basement, or main floor ceiling.
Oh, how I wish they made an electronic stud finder that would scan into the two layers of hardwood and subfloor. But as of this writing I know of none that will function well without many false readings.
If you are unlucky enough to have the hardwood running in the same direction as the floor joists, you will only be able to re-nail one strip of hardwood every 16" (as the joists are spaced). This will quiet a squeaky subfloor a bit, but you may have to nail between the joist with 2" finishing nails in an attempt to quiet the loose hardwood in between the joists. In this case working from below with the Squeak Enders product may be the best idea. Even if you have to bring down part of the basement ceiling. I guess it depends on just how determined to are to silence your floor.
Once you have marked out all the joists with the chalk line, determine which side of the hardwood strip is the tongue side. You will want to pre-drill or "nail spin" a 3" spiral finishing nail, so that this nail goes through the tongue side of the hardwood floor board through the subfloor, and penetrates the joist quite solidly. Nail spinners are a must and are available at http://www.leevalley.com Prod. #99K20.01
The nail should be spun in at about a 45-degree angle, the same as a new floor installation. This 3" nail should be only used for 3/4" thick floors, use shorter ones for thinner strip floors. A 2 1/2" nail should be used for 1/2" and 3/8" hardwood strip floor so as not to crack the tongues. The nail spinner works wonders for this application, I dont do repairs or installations without it. But be sure to use the spiral or "ardox" type nail in this use.
Modern floor joists are much less than 2" wide so they are easy to miss. Again, you can tell when you are hitting the joists when the nailing feels solid all the way in. Set the nail below the surface with the proper sized nail set, and fill with colored filler. Use colored latex filler that will dry hard if you plan on sanding the floor now. If this is a finished or prefinished floor that will not be sanded later, use the latex filler with care. Be sure to wipe off all excess with a wet rag, then a dry rag. This will prevent an unsightly smear on the finished wood. Choose a color just slightly darker than the finished wood. With the latex fillers I find I can come back the next day and apply a careful drop of floor finish on the filled hole to make it look more like the finished wood surface.
Or you can use non-drying oil based putty, whose excess is wiped off with paint thinner or mineral spirits. You cannot apply a finish to these types of putties. Putty sticks have this kind of putty in them.
You can do this renailing on every sixth board or so and see how it works. Then put more nails between these if you need to. Don't over do it, or you will have a really pock marked floor. But if the hardwood boards are really gapped this may not be noticeable at all, once you set the nail deep in this gap.
What do you think, is all this worth while? I think it is. Its got to be a lot easier than removing the hardwood, renailing the subfloor, and replacing the floor with the same wood or new floor. But for the really ambitious readers this is possible too. Ill describe now the tools and methods for removing an old gapped and squeaky hardwood floor, without wrecking it. Just make sure the old floor that your are trying to salvage is still thick enough to survive the removal, and later the sanding process.
You remove an old floor the opposite way it went in. Start at the far end of the room where the last few boards were laid. They will have their tongues pointing toward the wall. The last 2-3 rows will be face nailed. You will only have to crack one board in half (with a chisel and mallet) in the last row to remove it. Then use a cat's paw restorer at:http://www.leevalley.com/wood/page.asp?SID=&ccurrency=1&page=32014&category
This tool will gently remove the boards without damaging them. Try to scoot the thin edge of the catspaw under where the floor is nailed, and pry just a little at a time. Once you work backwards into the room and get some maneuvering space you can use a larger tool: http://www.leevalley.com/wood/page.asp?SID=&ccurrency=1&page=32015&category
The renovator bar will ease up the most stubborn boards.
Once you have the whole floor removed, re-nail and repair the subfloor, so that when the hardwood goes back, it will be squeak free. Re-nail the subfloor with the spiral spikes that are at least 3 times the thickness of the subfloor. A one-inch thick pine plank subfloor needs 3" nails to refasten it to the joists. A subfloor board 4-6" wide needs two nails on EVERY joist. Wider subfloor boards need 3 or even 4 nails to firm them up. This is the last chance you have to fix the subfloor. Oh, and even a plywood subfloor needs renailing, as often the original builder skips joists and has the nails too far apart. The nails should be every 6" or so, on plywood.
I use a pneumatic framing nailer when I take this step before installing a new floor. But I am careful to set the pressure so the nail heads end up slightly proud of the surface. I go back over those rows after the magazine is empty and pound these nails flush with the surface with my 20 oz. decking hammer. This does two things: it assures that the nails will not be over pressured and set too deeply into the wood, thus damaging the strength of the subfloor. Also the pounding releases most of the dust and debris that may be caught between the subfloor and the joist. That way my new floors are always squeak free.
If your are unlucky enough to have a water damaged OSB subfloor that is causing some popping and squeaking, consider adding 3/4 plywood over it, as a superior nailing surface. Or I would simply (sorry, not simply but really expensively!!) replace the OSB with plywood. This is a complex issue and I address subfloor requirements in the Strip Floor article in this Paid series of articles, be sure you read it, if you have OSB as a subfloor and it squeaks or pops as you walk across it.
These additional articles on plank and strip floor will help you determine just what fasteners to use and what subfloor requirements your salvaged floor will need. After all that work or removal, it would be a shame to have it squeak again. Whenever I re-nail a subfloor (before I lay a new hardwood floor) I always walk over the floor to make sure it is squeak free. Again, its just too late when the new floor is installed.
Here are just a few more suggestions before I close this article. You will see a lot of fairly lame solutions in stores to quiet squeaky hardwood floor. Please stay away from the long snap off screws, which are better suited on carpeted floor. They can easily crack the hardwood, or snap off halfway in. They may seriously mar the surface of a prefinished wood floor.
Shims under the floor are only used if there is a low spot in the floor. Which is rare. If you pound in a shim under the subfloor, you may muffle a squeak, but cause a permanent hump in the finished floor above. If you find that a subfloor board is cracked or not meeting the joist (when you view it from underneath) this would be the case to screw a ledge of plywood to the joist to correct this. You might even consider a bridge of plywood between the joists held up by two ledger boards, if the subfloor is really damaged.
But for general squeaks nailing a ledger board to the side of the joist is rarely as effective as using the Squeak Enders products I mentioned before. And as of this writing they have not paid me a cent to mention their products, except to give me samples, which work quite well.
So there you have it finally the definitive article on how to cure those annoying squeaky wood floors. Im finally finished this after having answered e-mail questions on this subject hundreds of times. I hope I have done this well.