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 machines.
Sanding Machines
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
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.
Sanding Procedures
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
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
professionals.
Surface Finishes
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.
Staining
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 wood floors.
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
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
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
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
full strength.
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 slippery.
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.