Wooden Floors - Sanding
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 mould 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.
Source:
Michigan State University
