State University Extension
Home Maintenance And Repair - 01500574
Wood Floors and Finishing
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 which can also supply the sandpaper.
Some handwork may be necessary in places that are inaccessible to power
Sanding machines may be either the drum type or disk type (floor
polisher). In 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
movement of the machine. In 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. A drum sander, however, can
not 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.
Sandpaper acts by gouging fine slivers 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, but the scratches left are too small to see. Scratches are
least noticeable when they run with the grain of a wood. Scratches must
be especially fine to escape detection on a 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 sandings with a 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 the sanding machine will not
be damaged. 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.
Note.- After the second or third pass, the floor may be buffed with
steel wool using a machine. However, steel wool should not be used 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 flooring where all pieces run parallel
to each other, all cuts may be made 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 450 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). Extra care should be taken to see
that each pass after the first is deep enough to remove all scratches
left by the previous sanding. The last pass should be made with
relatively fine sandpaper.
Regardless of the type of floor being sanded, an edger should be used
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, the floor
should be inspected carefully to see that all blemishes and visible
scratches have been removed and that a smooth surface has been
produced. Defects can be seen most readily if the floor is viewed
against 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.
If an old finish cannot be satisfactorily repaired, 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 a number of
sandings. 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 heat and abrasion of the
sanding operation may make the old finish gummy and will quickly clog
normal sandpaper. Once new wood appears, regular sandpaper may be used.
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 for new flooring. If
the floor is less than 3/4 inch thick or if it is made from hardwood
plywood, care must be exercised to prevent sanding through to the less
desirable wood beneath. The floor thickness can usually be determined
by removing a floor heating register or the shoe mold and baseboard so
that an edge of the floor is exposed. 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.
Finishing a wood floor is perhaps one of the most critical but
rewarding steps. Finishes are applied to wood for two principal
reasons. First, a finish should protect the wood from damage such as
stains, moisture and mechanical wear. Second, a properly applied clear
finish will accentuate woods' natural beauty and color. Penetrating
seals (sealers) and surface finishes are the two principal types of
protective coatings used on wood floors. Either will give satisfactory
performance if applied correctly.
Penetrating seals are probably the most common finish on residential
floors. Sealers are usually thinned varnishes which, when applied to
wood, will penetrate into the wood pores on the surface. The result is
usually a low gloss or satin finish that wears only as the wood wears.
The eventual effects of traffic are far less apparent than with other
finishes that only coat the surface. Scratching and chipping of this
finish is not a serious problem. One coat of a penetrating sealer can
give satisfactory performance, but two coats are generally better.
There are two basic types of sealers. Normal (slow drying) sealers can
be used successfully by most anyone. Fast drying sealers are more
difficult to use since it is easy to form lap marks or a splotchy
appearance. Therefore, they are usually applied only by experienced
Surface finishes which are relatively easy to apply and will give
satisfactory service include polyurethanes, varnish, shellac, lacquer
and some others. The polyurethanes are some of the most popular surface
finishes because of their high resistance to moisture, mechanical wear,
stains and spills. They are available with a high gloss or matte
finish. Polyurethanes are either oil modified or moisture-cured. The
oil modified types are the easiest to apply.
Varnishes can also give satisfactory performance. However, varnishes do
have a greater tendency to scratch, and worn spots are difficult to
patch without showing lines between the old and new finish. Varnishes
specifically designated for floors tend to be more durable. A glossy or
matte finish is available. Varnishes may be based on phenolic, alkyd,
epoxy or polyurethane resins. Shellac and lacquer are sometimes used as
floor finishes. These finishes will dry rapidly, and more than one coat
can often be applied in the same day. However, shellac and lacquer are
not as resistant to moisture, spills and mechanical wear as are the
penetrating sealers, polyurethanes and varnishes.
Surface finishes will usually give a longer life than penetrating
sealers without any attention other than regular sweeping or dry
mopping. However, when surface finishes must be renewed, it is usually
necessary to refinish the entire room.
In most cases, it is preferable to maintain the natural color of
hardwood floors by using a clear finish. However, if a color different
than the natural wood color is desired or if the natural wood color is
too variable, a stain may be used. Stains do not penetrate wood deeply,
and they may fade with continued exposure to bright light. Open grained
woods such as oak, ash, pecan and walnut will take stain easily while
the close grained woods such as maple, and to a lesser extent, birch
and beech, will take stain much more slowly. Soft-woods do not stain
well since the less dense springwood easily stains dark whereas the
dense latewood will hardly stain at all. Be certain to use
"non-grain-raising'" stains. Take the same care in cleaning and
preparing a surface to be stained as would be done in finishing it.
Oil-based pigmented wiping stains are probably the most common. The
pigments are in suspension so the material must be stirred regularly
during use to maintain a uniform color. The pigment collects in the
open pores of the wood and thus accentuates the grain pattern and
alters the wood color. Pigmented stains are usually applied by
brushing. After the stain has penetrated the surface and the desired
effect is achieved, all excess is wiped off with clean rags. Colored or
pigmented penetrating sealers are also available. In this case, the
pigment is mixed with the sealer, and both are applied at the same
time. Pigmented penetrating sealers will not obscure the natural wood
grain or shorten the life of the floor. Varnish stains are similar to
penetrating sealers since the coloring pigment is formulated with the
varnish. Therefore, the wood is colored at the same time it is
finished. Since the coloring pigment remains in the varnish as it cures
on the surface, much of the natural wood grain and color is obscured.
Certain application precautions are necessary to appropriately finish
1. Dust and dirt are an important factor in causing a rough surface.
When applying the first coat of finish, be certain that the wood is
perfectly clean and free of dust, dirt and other foreign materials.
Dust and dirt must also be removed from cracks or other floor
irregularities. The walls, windows and doors should also be cleaned to
keep dust motes from dropping into wet finishing materials to mar their
appearance. A painter's tack rag or turpentine-dampened rag will help
pick up much of this dirt. A careful cleaning is also necessary before
a second or third coat of finish is applied.
2. Most finishes will not stick to wax, oil and other materials which
may contaminate the surface. Be certain that the finish is applied only
to bare, clean wood.
3. The temperature of the floor, room and finishing solution should be
about 70 degrees F or somewhat warmer to assure that the finish flows
on evenly and cures properly.
4. Most finishes cure faster in dry weather. Therefore low humidity
conditions are also ideal.
5. A rough finish can also result if dust or small piece of dried
finish are transferred from an old applicator or from a partially used
can of finish. For each job, it is probably best to start with a new
applicator and supply of finish.
6. Provide adequate ventilation to carry off any fumes.
7. Application of finishing materials should begin promptly after
sanding so that there will be no time for changing moisture conditions
to raise the wood grain.
Penetrating sealers are best mopped on using a clean string mop or
long-handled applicator with a lamb's wool pad. Apply generous amounts
of the sealer, making sure that final stroking is in the direction of
the wood grain if possible. Any excess sealer which remains on the wood
surface should be wiped up with a clean cloth or squeegee. A wide brush
can also be used for application. After the first coat has dried it
should be buffed with No. 2 steel wool. Buffing can be done by hand or
with an electric polisher equipped with a steel wool pad. A second coat
of penetrating seal will result in longer service life, but is not
always necessary, particularly on close grained woods. Penetrating
sealers can usually be refinished in heavy traffic areas without
showing patch marks.
Polyurethanes may be applied using a brush or lamb's wool applicator.
Because polyurethanes are a surface finish, care should be taken to
work along the grain. Polyurethanes should be flowed on in a continuous
manner so that the leading edge does not have time to dry out. After
the first coat is thoroughly dry, buff it with steel wool, dust well
and then apply the final coat.
Varnishes are usually applied with a brush and flowed on evenly and
smoothly. The first coat can be thinned lightly so that it will
penetrate into the wood like a sealer. After the first coat has dried,
smooth it with fine sandpaper, dust well and then apply the top coat
For the final touch of beauty and to protect the finish, apply one or
more coats of good wax recommended for use on floors. Use either a
liquid buffing wax/cleaner or paste wax. Use only brands that are
designated for hardwood floors and if a liquid, be sure it has a
solvent base, not a water base.
Apply the wax after the finish coat is thoroughly dry and polish it
with a machine buffer. The wax will give a lustrous sheen to the floor
and form a protective film that prevents dirt from penetrating the
finish. Some manufacturers of urethane finishes do not recommend
waxing, especially for commercial jobs, because wax may make the floor
Wood floors finished with penetrating seals are not too difficult to
repair should they show early signs of wear in the traffic channels or
become stained or water damaged in localized areas. Floors finished
with polyurethane or varnish can also be repaired, but lap marks or a
splotchy appearance is more difficult to avoid. Floors finished with
lacquer or shellac are nearly impossible to repair successfully.
Finishes are best renewed when they begin to show signs of wear in
traffic channels but before the bare wood is exposed. In this case, the
floor must be cleaned of all dirt and debris, and all floor wax must be
removed as it may interfere with the drying and adhesion of any new
finish. Most of the wax can be stripped with rags kept moistened with
mineral spirits or other paint thinners. The rest of the wax should be
washed off with soap and warm water, doing the work as rapidly as
possible so that the water will have little time to contact the wood.
After the surface has thoroughly dried, a new finish may be applied.
If a penetrating seal is being restored, apply it to the worn areas as
already described. Be careful to wipe up any excess, particularly in
those areas where the old finish is still in good repair. If a surface
finish such as polyurethane or varnish is being used, it may be a good
idea to apply one coat of finish to the worn areas first. End all brush
strokes at joints between boards. After the first coat is thoroughly
dry, apply a second coat over the entire floor.
If only a small stained or water damaged area is being repaired, try to
remove the discoloration first. Use steel wool or a fine grade of
sandpaper to smooth out the affected area and an inch or two of the
surrounding floor. Remove all dust. Then brush on one or more thin
coats of finish, feathering it in to the old finish to prevent lap
marks. All plenty of time for drying between coats. Wax the repaired
area if appropriate.
This article was written by Anne Field, Extension Specialist, Emeritus
with references from Finishing & Maintaining Wood Floors North
Central Regional bulletin, Purdue Extension and the U.S. Forest
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status. Issued in furtherance of MSU Extension work, acts of May 8 and
June 30, 1914, in cooperation with the U.S. Department of Agriculture.
Thomas G. Coon, Director, MSU Extension, East Lansing,MI 48824. This
information is for educational purposes only. Reference to commercial
products or trade names does not imply endorsement by MSU Extension or
bias against those not mentioned.
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