How-to Polyurethane a Floor
Polyurethane is tough finish, suitable for floors, that is fairly easy to apply. It is available in oil and water based
varieties. We've seen both look good (for a short discussion of the two,
see below). In addition, polyurethane is available in a
gloss, semi-gloss and satin sheens. I prefer satin but it is a matter of taste. If you are unsure, buy a little can of each and try
them on a scrap. Two notes, always stir polyurethane, never shake it and make sure you have adequate ventilation.
Prepare the surface. If you need to sand the floor first, see the Floor Sanding project.
Vacuum the floor (Fig. 1) and wipe it
down with a tack rag (Fig. 2). Make sure that you remove all of the debris on the floor.
Step 2 (optional):
First thing: make sure that the stain you use is compatible with the polyurethane that you are using. If you are
unsure, contact the manufacturer. Many people like to apply a stain to the floor before finishing it. Many times a very light
stain called "natural" is used but it is a matter of personal taste. The floors in this how-to have been stained with a walnut
stain that is very dark. Apply the stain to the floor with a brush or rag. If you are using a rag, wear rubber or latex gloves
(rubber holds up longer). Work from one side of the room to the other (Fig.
3), making sure that you don't get
trapped into the room (Fig. 4)! Wait until the stain is dry (check the package) and then go over it with a clean rag. If you don't want the stain
to penetrate fully, work in patches, applying the stain and wiping the excess off a few minutes later.
Now you have to "seal" the floor. This is done by applying a thinned-out ("cut") layer of polyurethane to the floor. You
thin the poly by mixing full-strength poly with the appropriate solvent. If you are using oil-based poly, you will likely use
mineral spirits. If you are using water-based, it may be water. Check the package for the appropriate solvent and ratio for the
mix. Apply the polyurethane with a brush or painter's pad.
Use even strokes making sure you cover the surface completely
(Fig. 5). Do not, however, "flood" the surface.
After the seal-coat has dried, lightly sand the surface using a medium-fine abrasive pad (you could also use very fine
sand paper or 000 steel wool for oil-based poly) to smooth the surface. Water-based polyurethane will "raise" the wood grain
and you need to smooth this out. Either kind of polyurethane will likely develop "dust pimples" and these need to be
leveled. Wipe down the floor with a tack rag after you are done.
Apply a coat of undiluted poly to the floor. Use the same method as above. If you look at the floor at an angle, you
can easily see any spots that do not have enough finish. After this coat dries, use a fine abrasive pad (or one of the
other alternatives) to remove any imperfections.
You should apply two more coats, sanding in between, to ensure that you get a good finish. Check the package for
instructions on when to recoat the floor.
When the final coat has dried, you should lightly wipe down the surface with a fine abrasive pad to remove any
imperfections. If you applied water-based poly, you can rub down the finish with a fine abrasive pad and water to get a final
smooth finish. Remember that the more you rub, the less glossy the finish will look. This isn't necessarily bad, it is just the way it
is. If you used oil-based, you can use some 0000 (extra-fine) steel wool for a final rub down. Either way, do not rub too hard.
Types of Polyurethane:
Water-Based: Many people like water-based finishes because they usually dry faster, smell less than others and
cleanup with water. Water-based poly appears milky-white in the container but dries clear. Some people dislike water-based
poly because the dried finish looks somewhat "cold" or "blue." This is generally remedied by using a tint in the
polyurethane. When using water-based poly make SURE that you do not use steel wool to smooth the finish. The small steel particles
left behind can rust and make your finish look bad.
Oil-Based: Most oil-based finishes make the wood they are applied on look "warmer." This is due to the solvents and oil
in the base. Oil-based poly smells more than water-based and usually dries a bit slower. It will also tend to yellow a bit