transparent coating when spread in a thin film over a
surface, affording protection and decoration.
Of the common types of varnishes, the most
important are the oils, including spar, flat, rubbing,
and color types. These are extensively used to finish
and refinish interior and exterior wood surfaces, such
as floors, furniture, and cabinets. Spar varnish is
intended for exterior use in normal or marine
environments, although its durability is limited. To
increase durability, exterior varnishes are especially
formulated to resist weathering.
Varnishes produce a durable, elastic, and tough
surface that normally dries to a high-gloss finish and
does not easily mar. Often, a lower gloss may be
obtained by rubbing the surface with a very fine steel
wool. However, it is simpler to use a flat varnish with
the gloss reduced by adding transparent-flatting
pigments, such as certain synthetic silicas. These
pigments are dispersed in the varnish to produce a
clear finish that dries to a low gloss, but still does not
obscure the surface underneath (that is, you can still
see the grain of the wood).
Shellac is purified lac formed into thin flakes and
widely used as a binder in varnishes, paints, and stains.
(Lac is a resinous substance secreted by certain
insects.) The vehicle is wood alcohol. The natural
color of shellac is orange, although it can be obtained
in white. Shellac is used extensively as a finishing
material and a sealant. Applied over knots in wood, it
Lacquers may be clear or pigmented and can be
lusterless, semigloss, or glossy. Lacquers dry or
harden quickly, producing a firm oil- and water-
resistant film. But many coats are required to achieve
adequate dry-film thickness. It generally costs more to
use lacquers than most paints.
Stains are obtainable in four different kinds: oil,
water, spirit, and chemical. Oil stains have an oil
vehicle; mineral spirits can be added to increase
penetration. Water stains are solutions of aniline dyes
and water. Spirit stains contain alcohol. Chemical
stains work by means of a chemical reaction when
dissolved by water. The type of stain to use depends
largely on the purpose, the location, and the type of
wood being covered.
LEARNING OBJECTIVE: Upon completing
this section, you should be able to describe the
procedures used in preparing surfaces for
The most essential part of any painting job is
proper surface preparation and repair. Each type of
surface requires specific cleaning procedures. Paint
will not adhere well, provide the protection necessary,
or have the desired appearance unless the surface is in
proper condition for painting. Exterior surface
preparation is especially important because hostile
environments can accelerate deterioration.
As a Builder, you are most likely to paint three
types of metals: ferrous, nonferrous, and galvanized.
Improper protection of metals is likely to cause fatigue
in the metal itself and may result in costly repairs or
even replacement. Correct surface preparation, prior
to painting, is essential.
Cleaning ferrous metals, such as iron and steel,
involves the removal of oil, grease, previous coatings,
and dirt. Keep in mind that once you prepare a metal
surface for painting, it will start to rust immediately
unless you use a primer or pretreatment to protect the
The nonferrous metals are brass, bronze, copper,
tin, zinc, aluminum, nickel, and others not derived
from iron ore. Nonferrous metals are generally
cleaned with a solvent type of cleaner. After cleaning,
you should apply a primer coat or a pretreatment.
Galvanized iron is one of the most difficult metals
to prime properly. The galvanizing process forms a
hard, dense surface that paint cannot penetrate. Too
often, galvanized surfaces are not prepared properly,
resulting in paint failure. Three steps must be taken to
develop a sound paint system.
1. Wash the galvanized surface with a solvent to
remove grease, waxes, or silicones. Manufac-
turers sometimes apply these to resist white
rust that may form on galvanized sheets stored