To Transform a Hardwood Floor, It’s Best to Start From the Bottom : Repair: Expect to take a week--for buying, cleaning, working and waiting--to get the job finished.

Refinishing hardwood floors takes time, but the results can transform a room. Allow at least a week for the job--a day to prepare the space and to gather materials and tools, another to sand and several more to apply finish and allow drying time between coats.

Here are the steps to follow. Caution:

Sanding dust is highly flammable. Don’t smoke or strike matches while sanding. Be sure pilot lights on nearby appliances are turned off. To avoid irritating your eyes or respiratory system with flying dust, wear goggles and a respirator mask while sanding. Wear earplugs to cut down on the noise, and gloves to protect your hands. Sanding:

1. Sanding is a messy job, even with a dust bag on the sander. Remove furniture, drapes and all other portable items from the room being sanded. Cover doorways, air vents and permanent fixtures with plastic sheeting. Seal closets with masking tape. Remove carpet staples from the floor and repair damaged or loose flooring. Drive nailheads well below the surface with a nail set and fill the holes with wood putty.

Remove as many obstacles--such as radiator cuffs--as you can. Carefully remove shoe molding, where the baseboard meets the floor. Number the molding pieces for easy reinstallation.

Vacuum, then inspect the floor once more.

2. Rent a drum-type sanding machine for the main floor surface and an edger sander for edges and corners. Use a sandpaper block where neither sander can reach. The usual procedure is to sand with three grades of sandpaper: coarse--or extra-coarse if the floor is in bad shape--followed by medium and fine.

3. Tilt the drum off the floor, turn on the power, then lower the drum carefully, keeping a firm grip on the handles. Sand the floor with the grain. Sand the length of the floor a strip at a time. After each strip, return to the beginning and do the next strip parallel to and slightly overlapping the first. Always keep the machine moving or the sander will “eat down” into the wood and leave an uneven surface.

Using a drum floor sander is like walking a headstrong dog. Your job is to let it pull you but not as fast as it can.

4. Sand floor edges immediately after drum sanding an area, as saving all the edges until last may result in a visible meeting line.

5. When you’ve finished sanding, sweep, then vacuum thoroughly. Next, damp-mop the floor to remove dust and raise the wood grain. Wear thick socks or white-soled sneakers to avoid marking the stripped floor. Applying finish:

1. If you want the floors to be only slightly darker than the bare wood, apply a penetrating sealer. If the floor is to have a darker tone, apply wood stain, preferably one combined with a sealer.

Use an inexpensive, long-handled foam rubber roller so you can throw away the roller instead of cleaning it between coats. Use a small brush for edges and corners.

2. When dry, buff with a rented floor-polishing machine equipped with fine steel wool. Vacuum thoroughly.

3. You can also apply polyurethane, shellac or varnish. Polyurethane is more expensive but provides a durable surface that is moisture- and scratch-resistant. Use the roller and brush to apply these finishes.

Apply three coats of polyurethane. Thin the first coat with one part mineral spirits to four parts polyurethane. Let each coat dry 24 hours before recoating.

After each coat has dried, buff with the floor-polishing machine equipped with superfine steel wool, then vacuum thoroughly. Allow two days drying time before the final buffing.

Observe ventilation precautions on the container.

4. Apply a paste polishing wax (never use a water wax) made specifically for hardwood floors. Use a soft cloth as an applicator and buff with a floor-polishing machine. Apply a second coat over the dry initial coat and polish it. Complete the job by replacing the shoe molding.

Some polyurethanes do not have to be waxed. Check the label. With a no-wax type, use wax only if you prefer a softer patina.

5. The floor finish needs time to toughen. Allow it to cure for a few days before moving everything back.