When finishing hardwood floors, sanding is incredibly important. Follow these tips and tricks to get the job done well.
Before you begin, make sure you understand some of the most common mistakes people make and learn to avoid them. Do not let the sander gouge the floor, make sure you remove all of the old stain, do not leave high spots or ridges, use and edge sandpaper and use a fine sandpaper.
Most oak floorings are 0.75-inch thick and can be sanded a number of times. Some may be thinner floors, which must be refinished with caution to avoid sanding through to the subfloor. Remove a floor register and measure the thickness of your flooring. If it is thinner than 0.75-inches, consult a professional floor refinisher.
If yours is a 0.75-inches flooring, you are now ready to begin sanding. This is the only difficult part of the entire process. You need to be very careful here or you can gouge the floor past repair. I have seen this happen to a friend who had not bothered to learn the proper use of the drum sander. Fortunately, the gouge was in an area covered by a sofa, but you do not want to start arranging your furniture according to your gouges.
When you rent the drum sander, be sure you get a manufacturer's instructional manual and some hints and a demonstration from the store where you rented it. Be sure it's in good shape and functioning well. Check to be sure you have all the dust bags, special wrenches, and attachments. The machine is powerful, and, if not used properly, can quickly gouge your floor beyond repair. If you feel you are not strong enough to handle the drum sander (it requires no great strength), ask someone else to help you. You may want to practice on a piece of plywood, or with fine sandpaper, until you get the hang of it. Always use a dust mask. Ear protection is recommended as well.
Purchase several grits of "open face" sandpaper. Coarse grits will be needed for the rough sanding and for removing the old finish. Finer grits will be needed toward the end of the sanding process to provide a smooth finish. If you need to remove paint or sand cupped boards, start with a 20-grit paper. To remove shellac or varnish, a 36-grit will do. For the second sanding, a medium, 80-grit paper is used; and the final finish sanding requires a fine, 100-grit paper. The actual number of sanding passes, from two to four, will depend on the condition of your floor and the build-up of old finish and wax.
Be sure to buy enough paper. The average room will require 10 sheets of each grade for the drum sander and 10 sheets of each grade for the disc sander. Get a surplus and return what you don't use.
Start by using the rough-grit sandpaper. You will not only be removing any previous finish, stain, or discoloration, but also leveling the floor to a smooth surface. There may be warped boards or ridges where the boards come together. If the floor is very bad in these areas, you may need to sand diagonally across the floor with a rough-grade sandpaper until the floor is smooth. Then sand with the grain of the floor to get out the sanding marks left by the diagonal sanding. Except for sanding these badly cupped areas, always sand with the grain of the floor.
Use a coarse grade in the beginning, unless the floor is in very good condition. Be sure the paper is properly installed and be prepared to change it regularly. The heat will melt the old finish, and this clogs the sandpaper.
As you begin sanding, remember never to turn the sander on while the sandpaper and drum are touching the floor. Tilt it back by the handle until it is out of contact. Start the sander, and, when it reaches full speed, slowly lower it until the sandpaper touches the floor. Begin to move the moment the drum touches the floor. Let the sander pull you forward at a slow, steady speed. You can sand both forward and backward, but always keep the sander in motion. Never allow it to stop while turning. Sand in straight lines along the grain pattern of the flooring. As you approach the end of your run, lift the sander while it is still moving forward.
We recommend sanding two-thirds of the floor in one direction and one-third in the other. Whenever you need to reposition the sander, be sure the drum is off the floor. Overlap your back-and-forth passes to be sure you are sanding all areas thoroughly and to assure an even finish with no sanding marks. Go forward and then return over the same area as you go backward. Move sideways in 3 to 4-inch increments to overlap each pass.
After you have done the main body of the hardwood floor with the rough paper, use an edge sander where the floor meets the wall and in other areas missed by the drum sander. Again you will be using coarse-grit papers. Follow the manufacturer's instructions with this machine because it can also gouge the wood, but not as easily as the drum sander.
After the first sanding, check to see if any nails are now protruding, and, if so, countersink them. Fill all dents, gouges, and cracks with wood dough and allow it to dry. Then repeat the process with both the drum and edge sanders with medium-grit paper.
Repeat this process for the final coat; but before beginning this coat, use a high-quality hand paint scraper to get to any areas the power tools could not reach, such as under radiators and in corners. Do a good job, because this determines the quality of the final finish. Also, if there are any nail holes, dings, or other holes in the floor, fill them with wood dough of a similar color as the flooring and sand flush with the floor surface.