Rent DIY-friendly sanding equipment
You most likely won’t be sanding tons of floors in your life time so renting random orbital sanders are the best choice for do-it-yourself floor refinishers. They take longer to remove old finishes than drum sanders, but they do not require a lot of experience to use and are less likely to damage your floor. With a random orbital sander, you can move with or against the wood grain. Just be sure to keep the sander level at all times. Even an orbital sander can “run away” from you and cause sander markings that are difficult to remove.
Don’t get too aggressive
Begin with coarse-grit abrasives sufficient enough to remove the old finish and most surface scratches. Try not to use grits coarser than 60; this will help prevent you from damaging the flooring. Proceed with abrasives that are gradually finer until you reach the desired degree of smoothness. (My preferred progression for a hardwood floor such as oak begins with 60-grit abrasive, goes to 80-grit, and finishes with 100- or 120-grit.) Sand like you are mowing the lawn. Proceed row by row, overlapping runs by half the sander’s width. You will have to make go over it numerous times with each grit.
Always remember the corners
A palm sander may be used to sand near baseboard moldings, but use a sharp scraper to remove any areas of old finish the sander may miss. Scrapers allow you to get into recesses without having to remove a lot of material with the sander.
Guard against dust and hair
After you have finished with the sanding step, remove all dust by vacuuming and wiping the sanded areas with a tack cloth. If you find a stray hair embedded in dried polyurethane and you still have at least one coat to go, lightly sand over the hair with a very fine (320) abrasive. Carefully dig out the hair with a pin or fingernail, if possible. Then re sand with the same very fine abrasive, taking care not to breach the stain layer. Upon recoating with poly, the hair mark will all but disappear.
Apply stain evenly
Apply stain evenly, especially over a large space. I find that the best technique involves applying the stain with an applicator to one small area at a time (about 18″ x 3′) and then rubbing off all excess with a rag. Avoid letting the leading edge of your job dry; you will end up with lap marks. Try using Oil-based stains as it tends to stay workable longer, rather than using a water-based stain.
Thin coats are better than thick
An easy way for the do-it-yourselfer is to roll on the polyurethane using a foam roller, preferably a high-density foam roller. The coat will be thin, even, and will quickly dry to a glassy smooth finish. Use a good brush for cutting in around the room perimeter.
Have an exit strategy
Start your applications along the wall opposite the door you intend to exit. Work in parallel rows toward the wall with the door. When you get close, you will have to change your work pattern and work from the end walls toward the door. This makes it tough to achieve uninterrupted smoothing strokes, so apply a little extra poly and count on its self-leveling properties for a smooth finish.
Hopefully this will help anyone who is thinking of keeping those beautiful hardwoods maintained and refined! Enjoy!