How you restain hardwood floors depends on how often you restain and whether or not the floor has been properly protected. In the best case, you can simply apply a new coat of stain, but in the worst case you will need to completely refinish the floor as well, which means sanding it back down to the base wood and then restaining and refinishing from scratch.
State of the Floor
Whether or not your floor is in good condition will determine if you need to refinish the floor or simply restain it. If your floor is relatively scratch-free and has been protected from foot traffic over the years (such as with an area covered by a rug or a shoe-free living room), you have nothing to worry about, but if the floor has been scuffed, scraped, scratched or otherwise marred, you will have to do more than just restain.
If you are only restaining the floor, you will pay no labor costs because you only need to purchase stain, but if a refinishing process is required, you can be looking at significantly more in terms of prices. Simple restaining only costs about a dollar a square foot, as of September 2011, but if you hire a pro to do a refinishing job, you can expect to pay between $2 and $4 per square foot for basic hardwoods. Specialty woods can raise the rate up to as much as $10 per square foot.
The materials needed to restain a floor are fairly basic, since you normally only need stain and paintbrushes or sponges and old rags. If you need to refinish completely, however, and you are on a budget, you can rent a sanding machine and floor buffer and do it all yourself. The costs compared to hiring a professional are between 50 percent and 70 percent less depending on where you live, the experience of the professional and the quality of materials you purchase. Of course, running the machines requires physical strength and skill.