Corrective Measures. Apply shellac, varnish, or aluminum paint to wood knots before painting. Do not paint
unseasoned wood. For metal, apply paint with a spray gun, holding the gun level so that an even coat is applied.
5-30. RUNNING AND SAGGING
Characteristics. An effect of ripples or irregularities in a film of paint, varnish, or lacquer is known as runs or sags.
Probable Causes. Runs or sags are usually produced by the application of a paint, varnish, or lacquer which has
been thinned excessively, or by the application of too much material. It is usually evident on a sloping or vertical surface.
Other causes are incomplete brushing or the use of a stiff brush.
Corrective Measures. Sand the surface until runs or sags have been removed, then recoat with material of the
correct consistency, taking care not to apply excessive amounts. Use a flexible brush for this operation.
5-31. SLOW DRYING
Characteristics. Although the time required for drying is dependent upon the type of paint, enamel, varnish, or
lacquer used, certain weather conditions may prolong the drying period. Paints which, under normal drying conditions,
are tacky or sticky for long periods (12 hours or longer) are likely to attract dust and dirt, to promote mildew, or to develop
checking or alligatoring.
Probable Causes. Cold weather retards drying. Drying agents also may lose their effectiveness in prepared
paints that are dark in color. The use of old thinner, or the use of inferior driers and thinners, are other factors frequently
contributing to slow drying of paint films.
Corrective Measures. Do not paint when the temperature is below 50°F (10°C). A standard procedure is to paint
a test area and let it dry overnight before adding additional drier to the paint. This is done to assure a correct drying
period. In cold weather, apply a thin uniform film on a dry surface.
Characteristics. The appearance of discolored spots on a painted surface is known as spotting.
Probable Causes. Color changes and loss of gloss in irregular patches may be caused by spots in the surface
which absorb oil from the paint unevenly. This may be the result of too few coats, or the lack of controlled penetration of
the paint, and may occur on new items which have been given only two coats, or an old item painted with just one coat.
In white paints, this is accompanied by the loss of gloss. Colored paints usually appear to fade when the oil is absorbed
unevenly. Spots are sometimes caused by nail heads which rust. Splashes of liquid on a freshly varnished surface will
cause spotting, and rain or hail on a freshly painted surface will also leave spots.
Corrective Measures. Apply an additional coat of paint. Apply paint during dry weather. The use of paint
containing zinc oxide is effective in minimizing spotting on older items. In cases of spotting due to rain or sandstorms,
sand off rough spots before repainting.
Characteristics. The reappearance of luster on a varnished surface which has been rubbed to a dull finish is
known as sweating.
Probable Causes. Sweating of a varnished surface is usually caused by inadequate rubbing to attain a dull finish,
or the application of a finish coat before the undercoats have thoroughly hardened.