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Everything You Need To Know About Sandpaper & Abrasives
How Does Sandpaper Work?
Sandpaper
works a lot like a saw, chisel, or any other cutting tool in your
shop. The particles on sandpaper are made up from a number of sharp
edges that cut the wood the same way a saw blade does. The only real
difference is that sandpaper, unlike your saw, can't be sharpened.
Not exactly. There are two different grades of sandpaper on the
market; Commercial and Industrial. The commercial grade is commonly
available at hardware stores and home project centers. The
industrial grade is usually available only through industrial supply
stores. It's made from higher quality materials and is designed to
be used in the rigors of the production line.
Sandpaper is Sandpaper, Right?
Not
exactly. There are two different grades of sandpaper on the market;
Commercial and Industrial. The commercial grade is commonly
available at hardware stores and home project centers. The
industrial grade is usually available only through industrial supply
stores. It's made from higher quality materials and is designed to
be used in the rigors of the production line.
What is grit?
When
talking about sandpaper "grit" is a reference to the number of
abrasive particles per inch of sandpaper. The lower the grit the
rougher the sandpaper and conversely, the higher the grit number the
smoother the sandpaper. This make sense if you imagine how small the
particles on an 800-grit sandpaper would need to be to fit into a 1"
square. Sandpaper is referred to by the size of its grit (i.e.
150-grit sandpaper).
The
following table is a general guide to the proper uses, although this
may vary from wood species to species.
So
what's the difference between Commercial and Industrial grades?
There are
three main components to sandpaper; the abrasive grit, the backing
material, and the bonding agents. Industrial grade sandpaper uses
higher quality components as well as tighter manufacturing
tolerances.
Abrasive
Grit Industrial grade sandpapers use abrasive
grit material that is stronger and less likely to break down or wear
out. Higher quality grits are often very finely graded to ensure
consistency.
Backing
Material Commercial grade sandpapers tend to use
craft paper or low-grade fabric as a backing material. Higher grades
of backing material are often made from fine cottons or polyesters.
Bonding
Agent The bonding agent is the glue that
attaches the abrasive to the paper's backing. Lower grades of
sandpaper are often made from hide glue, which doesn't hold up well
with heat or moisture. Higher-grade bonding agents such as phenolic
resin are used for industrial grade sandpapers.
I've heard woodworkers talk about "Going through the
grits". What does this mean?
"Going
through the grits" is not a reference to eating breakfast in
Georgia! It refers to the process of sanding a work piece where a
woodworker uses progressively finer pieces of sandpaper to get a
smooth finish. By going through the grits each progressive piece of
sandpaper removes the scratches from the previous piece. Skipping
grits to save time is not necessarily a good idea. You will often
end up sanding longer just to remove the scratches left by the
previous grit. This is more important with harder woods like maple
than it is with softer woods like pine.
When
Can I stop Sanding?
In most
cases you can stop sanding at 150 or 180-grit. If you plan to use a
water-based stain it's best to sand up to a 200-grit sandpaper. This
is because water based stains can tend to pickup and magnify a
scratch. It can also be a waste of time to sand with very fine
sandpaper. Sanding maple with 400-grit sandpaper, for example, will
tend to seal off the grain and prevent finishes from penetrating.
What's the difference between "Open-coat" and "Closed-coat"
sandpaper?
Open-coat
sandpaper has gaps and open spaces between the grits that helps
prevent clogging by giving the sawdust a place to go. Open-coat is
most often used for woodworking. The spaces in the sandpaper can
cover 40-60% of the sandpaper's surface. Closed-coat is better for
sanding metal and wood finishes but clogs easily with sawdust.
Steel Wool:
Steel wool
begins life as a 3,000-lb. roll of 1/8-in.-dia. steel wire. This
wire is drawn across serrated knives that scrape off tiny wire
shavings from the larger wire. These shavings are carded into an
irregular, interlocked steel-wool mat, which is formed into rolls or
pads and cut to final shape. The larger the diameter of the
shavings, the coarser the texture of the steel wool.
Steel wool
is graded in a numerical "aught" (a bastardization of the word
naught or zero) scale, the coarsest being graded 4 and the finest
graded 0000 (pronounced four aught). Mostly, I use two grades of
steel wool, 0000 and 3. I use 0000 to rub finishes, apply wax and
clean hardware. I use 3 sometimes when stripping finishes. There are
times that I'll use 000 also, when I want a duller finish while
rubbing out.
Scotch- Brite Pads:
About 20
years ago, the Scotch-Brite dishwashing pad was introduced by the 3M
Co. Made from a non woven plastic, the pad has real sandpaper-type
grit (aluminum oxide or silicon carbide) impregnated throughout its
1/8-in. thickness. Unlike steel wool, the grade of the pad is
determined by the coarseness of the grit, not by the thickness of
the individual plastic strands. It quickly became obvious that this
material had some real advantages over steel wool. The tough
synthetic pad doesn't tear apart or shred little bits of metal wire,
making it ideal for sanding between coats of finish and, in
particular, on items such as chairs and table legs, where broken
bits of steel wool collect. Like sandpaper, the pad does shed some
abrasive particles, but a gentle blast of compressed air or a swipe
with a tack cloth removes them.
