Floor sanding can be done by hand, but electrically driven sanding machines are used almost exclusively today. These machines are usually available from rental agencies and some paint stores/home centers that also supply the sandpaper. Some handwork is usually necessary for less accessible places. Some safety practices should be respected when redoing a wood floor. You should wear a particle mask to protect you from inhaling dust, equip some safety glasses, and make sure to have good ventilation if you're using chemical removers.
Sanding machines may be either the drum-type or disk type (floor polisher). With drum sanders, the sandpaper is mounted on a cylindrical drum that rotates on an axis parallel to the plane of the floor. Thus, the sandpaper makes its scratches in straight lines in the direction of the movement of the machine. A drum sander, however, cannot reach the last few inches of floor nearest the baseboard. Electric edgers, which are small disk sanders, are available for sanding these edges of the floor, or they may be done by hand.
With disk sanders, the sandpaper is mounted on a disk that rotates in a circle in the plane of the floor. As a disk sander is moved over the floor, the grits make spiral scratches that necessarily cross the grain of the wood.
Sandpaper acts by gouging the topcoat finish from the wood surface, leaving scratches, the size of which is governed by the size of the grits on the paper. Coarse grits act rapidly, but the scratches they leave are conspicuous, especially if they cross the grain of the wood. Fine grits act slowly and require more frequent changing, but the scratches left are too small to see. Scratches are least noticeable when they run with the grain of the wood. Scratches must be especially fine to escape detection on wood with close texture, such as maple, and must be still finer to remain unnoticed if they cross the grain of the wood.
In sanding a floor, time is saved by starting with coarse sandpaper to remove the grosser roughness and imperfections and to make the floor level as quickly as possible. The scratches left by the coarse grits are then removed by successive sanding with finer sandpaper. The scratches left by the last paper should be too small to be observed even after the finish has been applied.
Before beginning the sanding procedure, carefully sweep all dirt, dust, and other debris from the floor. "Set" all nails that may be protruding either in the floor or baseboard so that errant fasteners will not damage the sanding machine. Sometimes, only two sanding cuts are needed on a new hardwood floor, but if the floor is at all uneven or if a particularly smooth finish is desired, three cuts will be necessary. The first cuts should be done with a coarse or medium abrasive, always ending with a fine abrasive. A smoother finish will result if the final sanding is done with the floor polisher or disk sander. Of course, more passes with finer paper will result in a smoother finish.
After the second or third pass, You may buff the floor with steel wool using a machine. However, you should not use steel wool on oak floors unprotected by finish because minute particles of steel left in the wood may later cause iron stains under certain conditions. When sanding strip, plank, or other floorings where all pieces run parallel to each other, you may make all cuts in the direction of the strips.
However, if the floor is at all uneven, one of the first cuts using coarse or medium paper should be at a 45-degree angle to the direction of the strips. This positioning will remove any peaks or valleys caused by minute variation in thickness of the strips or in the subfloor. When sanding parquet, block, herringbone, and similar flooring, it is necessary to cross the grain of many pieces with each pass. In these cases, begin sanding on a diagonal from one corner of the room to the other. The next cut is started from one remaining corner to the other, and the final cut is made at approximately 45 degrees to the first cut (from one wall to the opposite wall).
you should take extra care to see that each pass after the first is deep enough to remove all scratches left by the previous sanding. you should make the last pass with relatively fine sandpaper.
Note: Regardless of the type of floor being sanded, you should use an edger after each pass to finish any areas which were not previously sanded, such as edges, corners, and areas around radiators. These areas may also be hand sanded. Before the sanding is considered complete, you should inspect the floor carefully to see that all blemishes and visible scratches have been removed and that a smooth surface has been produced. you can see defects most readily if the floor is viewed against the light at a low angle of incidence so that any ridges will cast shadows. Any defects left at this time will show much more prominently after finishing materials have been applied.
Removing Old Finish
If you cannot satisfactorily repair an old finish, a complete sanding of the surface and then application of a new finish may be necessary. Most flooring is 3/4-inch thick, so it can withstand sanding. In these cases, make certain that all nails are countersunk and that the floor is as clean as possible before sanding. Use an "open face" paper to remove the old finish. The sanding operation's heat and abrasion may make the old finish gummy and quickly clog normal sandpaper. Once new wood appears, you may use regular sandpaper.
The number of cuts required to restore an old floor is largely determined by the condition of the floor and the thickness of the finish being removed. If the floor is badly scarred or warped, use as many cuts as necessary to get a smooth, unblemished surface. Make the first one or two cuts at a 45-degree angle with medium grit paper, and then follow the instructions given for sanding a new floor. If the surface is in good shape and has no thick build-up of old finish and wax, one pass with the disk sander and extra-fine paper may be sufficient. Just be sure that you have removed all the old finish.
Old finishes may also be removed with a non-aqueous (no water) varnish remover, after which the floor should be sanded as you would do for new flooring. If the floor is less than 3/4 inch thick or if it is made from hardwood plywood, you must exercise care to prevent sanding through to the less desirable wood beneath. you can usually determine the floor thickness by removing a floor heating register or the shoe mold and baseboard to expose an edge of the floor. When refinishing these floors, a chemical varnish remover may be useful. It will also help to use a floor polisher or disk sander rather than the drum sander. Do not remove more wood than absolutely necessary.
As you can see, wood floor sanding has multiple purposes. Now it's time for the finish!