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Finishing With Shellac
Shellac has been used as a woodworking finish since the early
1800's. It has many advantages: shellac is non-toxic, can be used as
a sealer before applying a stain (to even out the stains
application), can be mixed with nearly any color, and is very easy
to repair in the event of damage from use.
That
being said, there are some drawbacks to using shellac as a final
wood finish. Shellac does not hold up well to heat or water, and it
dries very quickly when being applied, which leads many woodworkers
to believe that applying a proper shellac finish can be difficult. I
actually find shellac to be very user friendly, as long as the
correct steps are followed and you practice patience.
What is Shellac?
Shellac is derived from a resin that is secreted from an insect
native to certain forests in southeast Asia. This insect secretion
is scraped from the bark of trees and, when processed, takes the
form of small, light-brown or orange flakes.
To
make an applicable woodworking finish, these flakes are mixed with
denatured alcohol. We commonly use a two-pound-cut finish, which is
to say a ratio of two pounds of shellac flakes per gallon of
alcohol. Pre-mixed shellac found in home centers may be three to
five pound cut, but this can be easily reduced (typically, the
measurements for cutting are listed on the can).
Applying Shellac:
There are two commonly accepted methods for applying shellac:
brushing and padding. To brush on shellac, use a fine, natural or
china-bristle brush. Use a two or three-pound cut of shellac and
apply generously with long, smooth strokes. Because shellac dries
quickly, be careful to avoid drips or blotchy areas when applying,
because unlike other finishes, you will likely not have time to
over-brush to eliminate the blemish.
Padding:
(Also...refer to our French Polishing post)
To apply shellac with a pad, use a clean piece of medium-weight
cotton muslin. The idea is to lay down a smooth, even application of
shellac in a single long, even stroke.
While many techniques for padding are used, a quick method is to
wrap a nine to ten-inch square piece of muslin or cotton around an
old (clean) athletic sock. Before beginning to apply the shellac,
place your cut of shellac into a squeeze bottle. Squeeze a liberal
amount of shellac into the sock to act as a reservoir. Then wrap the
muslin around the sock and hold the edges of the muslin behind the
sock.
Squeezing the pad lightly should allow a small amount of shellac to
seep through the muslin. The exposed shellac on the muslin surface
of the pad should be even with no dripping.
When
applying the pad to your woodworking project, you may need a bit of
a lubricant. Mineral oil or linseed oil works great, as it will not
affect the final color or finish. If your padding movement seems a
bit "sticky", keep a small bowl with a little bit of mineral oil
handy for light dipping. With a very small amount of mineral oil on
the loaded pad, you're ready to begin applying the shellac to the
wood. To start, do not place the pad directly onto the wood and
begin rubbing; instead, ease the pad on and off the stock to avoid
any blotchy spots. The best way to describe the motion is to work
much like an airplane taking off and landing.
Once
the pad is on the wood, work in somewhat irregular patterns rather
than just with the grain. This will insure a thorough coverage. As
you need more shellac, simply squeeze the pad a bit. A more
traditional method of padding is to fold a piece of muslin a few
times so you have a flat pad with a few layers of thickness. Then
apply light coats of shellac with a moist, but not dripping wet pad.
No
matter which method of padding you choose, you'll find padding works
best on flat surfaces. Irregular areas, corners and trim will likely
be easier to apply with a brush.
Many
woodworkers like to use a combination of brushing and padding. They
will apply the shellac with a brush, then immediately smooth it out
with a piece of muslin. Use long strokes moving with the grain of
the stock.
Completing the Shellac Finish:
After the first coat of shellac dries, lightly sand with 400-grit
sandpaper. Wipe off the white residue and apply a second coat.
Repeat until the desired number of coats have been applied.
This direct application will result in a high-gloss finish. If a
less glossy, satin finish is preferred, try buffing out the final
coat with some 0000 steel wool and (non-silicon based) paste wax.
Lightly work the wax over the finish until it is thoroughly covered.
Allow the wax to dry, then wipe off and buff to a lustrous finish.
Clean-up :
Brushes can be easily cleaned after applying shellac with alcohol,
as this will effectively cut the shellac until the brush is clean.
However, I find a simpler method is to clean the brush with ammonia.
The alkaline ammonia dissolves the shellac quickly and easily. After
the shellac is completely gone, wash the brush in soap and warm
water to keep the bristles soft. Dry the bristles and store the
brush in the container in which it came (to keep the bristles in
proper shape).
Repairing Shellac Finishes:
Shellac finishes should be kept
away from water, as they will become dull or even have a white
residue appear when exposed to moisture. Should your shellac finish
develop water spots, repair is relatively simple. Use straight
alcohol on a pad and remove the shellac from the offending area.
Then pad or brush on a series of coats of shellac and rub it out
until the finish is even.
Should a surface scratch appear through the finish, use a fine
artist's brush to fill the scratch with shellac. Rub out the finish
to even out the color between the repaired scratch and the
surrounding finish.
