Finishing normally begins about 7 to 14 days after installation. This gives enough time for the installed floor to react to the environment. Slight cracks and any raised edges that are going to develop will have done so by then, and you can fill and sand them for the best possible appearance. Longer periods of exposure may subject the bare wood to job-site abuse and moisture.

For starters, heart pine is naturally hard and dense, and the new polyurethane finishes offers increased protection wherever you install your wood floor. But there is a lot of technical know-how needed for polyurethane or any other hardwood floor finish. The finish industry is evolving rapidly to meet strict new regulations and the increase in demand for wood floors. If you have further questions, telephone numbers, books, and articles are listed in the back of this guide, all of which provide more detailed information.

Sanding

Just like site conditions are to installation, good sanding techniques are critical in finishing. If the sander leaves swirls or grooves these will become more noticeable once the finish is applied. Sanding creates a lot of dust. Wear a respirator, ear plugs, and shoes that do not hold dust in the soles or leave scuff marks.

The job takes at least a couple of different machines. A drum sander is used to level the floor, and a disc sander to “screen” (or lightly sand) between each coat. You might want an edger, a small floor sander that lets you get close to walls, or you can sand these hard to reach areas by hand. A professional floor finisher will have all of these machines, or you may be able to rent them from your local hardware store.

Seal off doorways, vents, and built-ins by taping plastic over them. Just before sanding remember to check for loose boards or squeaks and repair them with screws from underneath the subfloor or nail through the floor into the joists. Set any nails at least 1/16″ deep and fill the holes with wood putty.

Operating a drum sander takes some practice. The machine is heavy but has to be moved along with a relatively “light” touch. If held in place for even a few seconds it will leave a dent in the floor. Sand in rows in the direction that the floor runs from left to right across the room. The drum sander takes a slightly deeper cut on the left side to allow you to feather the edge on the right side as you move over to the next row.

Turn on the machine and move forward as you lower the drum to the floor so it does not dent the starting spot. You do not have to bear down at all. About one foot away from the wall, lift up. Put the machine down again as you begin to move it backward over the same row. When you reach the spot where you started, lift up and move over 2–4″ for each succeeding row.

The first “cut” (sanding) is to level the floor. Use a drum sander with coarse-grit (20-36) paper. Fill any nail or peg holes and sand again using medium-grit (50 to 80). Check for any more blemishes and fill them before the final sanding with fine-grit (100-120) paper. Scrap the corners and hard to reach places, then hand sand them to blend with the rest of the floor.

You will not be able to get close to the wall behind you, so plan to start a few feet away from the back wall and sand to within a foot or so of the wall in front of you. Then turn around and sand the few feet remaining to the other wall, again starting from right to left. Take care to feather over the line where you reversed directions. Use an edger to get the area that the drum sander could not reach at walls and under counters. You may need to use a hand scraper and hand-sanding block for some areas.

After the first sanding, sweep well and change to medium grit (60-80) paper and sand again. You may choose to use a filler between sandings, usually used when refinishing old floors. If you defects that you want to cover there are some good latex fillers available. Use fine grit (100-120) sand paper for the final sanding.

As soon as you have completely sanded the floor to a level surface, vacuum thoroughly and then wipe it with tack rags. Be sure to get all the dust from not only the floor and out of the corners, but also off windowsills and mouldings. Remember to clean out any vents as well. This will prevent sawdust from falling into the finish and becoming a permanent part of your floor.

“Wash” the floor with a rag or mop that has been dampened with mineral spirits. This is an important step for heart pine. It removes any oils or resins from the surface of the wood that might prevent the finish from adhering properly. The mineral spirits will dry within a few hours, unless applied too generously.

Supplies to Have On Hand for Finishing

Penetrating oil-based sealers can be applied by hand with a rag, a brush, or a lamb’s wool applicator. Surface finishes are usually applied by applicator, or by brush in small areas.

Between coats of surface finishes you will need an abrasive nylon screen, fiber buffing pad, or steel wool to lightly sand the previous coat and help the next one adhere. Do not use steel wool if you are using a water-based finish. The steel fibers will rust and discolor the finish. If you use brushes, clean them only with water or mineral spirits. The distillates in some brush cleaners can slow the drying process.

Use a vacuum cleaner after each sanding or screening. For large areas, clean vacuum bags frequently to avoid returning any dust to the floor. You might even try wearing paper surgical booties over your shoes to avoid tracking dust. Rags with mineral spirits or water are also useful to clean up sweat, dust, dirt, or oil if any drips on the floor while you are applying the finish.

When do I Apply the Finish?

People generally prefer the natural look of finishes applied in the home over a factory baked-on finish, and most fine wood floors are sanded and finished on-site. For best results, finish the floor after the wall coverings are in place and painting is complete, except for a final touch-up coat of paint on your base moulding.

Which Finish do I Use?

  • Water-based (or water-borne) urethane is a good choice for the environmentalist and is the easiest to apply. Water-based is only slightly less hard than moisture-cure, and is less likely to leave drying lines during application.
  • Moisture-cure urethane is the hardest and most protective finish, but it requires the most skill to apply. Generally, it is not suggested for use by the non-professional.
  • Traditional oil-modified polyurethane finishes are used today, though they will be regulated out of use in the future. Wax is generally applied on top of this finish.
  • Use a penetrating oil sealer for a natural but soft finish. Buff the floor with steel wool between each coat, and then wax over the sealer. This finish may be the correct choice for some projects, but it requires extra maintenance and offers less protection.
  • There are completely natural finish products available for people with chemical sensitivities or for those who want to use totally non-toxic products. Organizations specializing in the most healthful and ecological building materials are noted at the back of this booklet.

The First Coat

We recommend that the first coat be an oil-based sealer to help bring out the red tones for which heart pine is so famous.

The oil-based sealer is a penetrating finish and soaks into the wood, unlike surface finishes such as water-based or moisture-cured polyurethane. The real beauty of the wood can be brought out right away by one coat of the sealer.

Heart pine is renowned for its unique color and beauty. Many heart pine lovers model the late Frank Lloyd Wright who said, “I like wood left alone, for the sake of wood.” Stains may actually muddle the wood’s strong grain patterns. However, if your project has special needs you can get the sealers in wood stain colors.

The finish is applied in parallel strips across the room with the direction of the flooring. Always maintain a wet edge and use a single gliding stoke along the length of your strip, “feathering” into the previous wet area. Work toward the light so that you can see your work, but do not worry about retouching missed areas if the finish has already begun to skim over. The next coat will fill in these areas.

Make sure your floor is completely dry before you apply the second coat since the sealer soaks into the heart pine. We suggest thinning it with 1/4 to 1/3 Mineral Spirits to give it maximum penetration. It has been our experience that this coat may take longer to dry than the finish manufacturer’s directions. We often find that it takes at least 24 hours for this sealer coat to dry. One customer says, “We think the labels should read, ‘dries in four hours unless you live in Florida where it takes two days.'”

If you are in a hurry use a moisture meter to see if the floor has returned to its pre-finish moisture content. Or, check for a thumbprint by pressing your thumb firmly against the floor (see Don Bolinger’s book, Hardwood Floors, available through Fine Homebuilding magazine).

After the First Coat

You have lots of choices for the second coat of finish. Water-based is increasingly popular. It offers quick-drying time, takes little maintenance, and is simple to recoat when wear eventually begins to show. Moisture-cured and oil-modified finishes are still used a lot today, even in this low VOC (volatile organic compound) age. For a simple but soft finish, wax on top of the sealer.

We generally recommend water-based urethanes because they are safe, durable, fast drying, and offer good protection for your floor. Water-based products are being continually improved to decrease their VOC contents and increase their durability. A water-based urethane used on heart pine over an oil-based sealer applied in thin coats is a very pretty finish. It looks similar to an “oiled” or hand-rubbed finish. Some woodworkers may hate to admit this, but many know it is -true and use this to their advantage. After the first and between each succeeding coat of finish, use a floor buffer fitted with a used 100-120 grit “screen” (rub two together if you do not have a used one) or hand sand small areas. You will have to hand sand corners and edges. Lightly sand the “top” off the finish.

You do not want to sand into the finish, and one or two passes over the floor is usually enough. All that is necessary is to take the shine off the finish to help the next coat adhere to the one before it. If the finish does not “powder” while you are sanding, it is probably not dry. Vacuum the floor and any sills and baseboards. Tack the floor again, then let it dry completely, and start your next coat.

Additional tips for finishing your hardwood floors

  • For the best possible adherence from coat to coat, use high-gloss for all coats except the last one. Many types of polyurethane are so hard that they do not adhere well to themselves. The high-gloss adheres best, so even if you want a satin finish use high-gloss. Use satin as your final coat and you will get the low-gloss (or semi-gloss) finish that you want with maximum adherence.
  • You can apply as many coats of polyurethane as you want. Usually two or three coats is enough, but we have had people ask if they can use several coats. Just remember to let each new coat dry a little longer than the previous one.
  • It is important not to wax a wood floor that has a surface finish (water-based or moisture-cured). If wax is used on these finishes, it prevents the ability to simply retouch the floor (screen or lightly sand to remove the shine and recoat it). If you wax on top of a surface finish you must sand the floor completely back to bare wood before recoating.

Special Floor Finishing Needs

If you are restoring a historic building, you may choose varnish to match an old finish. We discuss varnishes in the section on “Refinish.” We can also provide you with reprints of Old House Journal articles about historic finishes.

You might want to know about finishes for porch or outdoor floors… or how to sand a parquet floor… or even how to “pickle” your floor. There are many topics, and we can only mention the basics in this short booklet. Do not hesitate to call with questions. We will try to provide other references.

There are many companies that make excellent finish products, a few are listed in the back of this guide. No matter which finish manufacturer you choose, follow their directions carefully. These products are improving rapidly as are the ecological standards they are required to meet.

Let us know if we can provide reprints of flooring manufacturer’s association guides on finishing to further assist you.

Other Finishes

We do not mention white floors nor do we discuss finishes that contain formaldehyde in this guide. These finishes are frequently used and many professionals have a great deal of experience with them. If you need to know about them, we can recommend sources.