coat is too thin, the remover may dry on the surface of
the metal.
You should allow the stripper to wrinkle and
lift the paint. This may take from 10 minutes to
40 minutes, depending upon the temperature, the
humidity, and the condition of the paint.
You should remove loosened paint and residual
paint remover by washing and scrubbing the surface
with fresh water, nonmetallic scrapers, fiber brushes,
or abrasive pads. If water spray is available, use a
low- to medium-pressure stream of water directly on
the surface while it is being scrubbed.
After you thoroughly clean the surface, you
should remove the masking materials and remove any
residual paint.
Rinse the surface with a freshwater and alkaline
solution (1 part MIL-C-25769 to 9 parts water) to
neutralize the paint remover.
FLAP BRUSH.—Paint can be mechanically
removed with a flap brush. The brush consists of
many nonwoven, nonmetallic nylon flaps bonded to a
fiber core. The brush assembly (fig. 14-29) is made
up of a flap brush, flanges, and a mandrel. It should
be operated by a NO LOAD, 3200 rpm, pneumatic
drill motor. The direction of rotation is indicated by
an arrow imprinted on the side of the core. When a
flap brush has been worn down to within 2 inches
from the center of the hub, you should replace it.
Continued use beyond this limit may cause gouging
due to loss of flexibility of the fiber. When you use a
flap brush, apply minimum pressure to remove the
maximum amount of paint and the minimum amount
of metal. Excessive pressure will cause some paints
to melt, gum up, and streak. Eye protection should be
worn when you are operating a flap brush.
SCUFF SANDING.—Aged paint surfaces
should be scuff sanded to ensure the adhesion of the
overcoating paint. Scuff sanding is the roughening of
a paint surface as evidenced by a significant reduction
of the gloss. To scuff sand, you should use aluminum
oxide cloth, abrasive mats, or an oscillating sander
with aluminum oxide cloth. Scuff sanding to a depth
greater than necessary may result in complete
removal of the paint. This situation will expose the
underlying metal, and corrosion may develop.
Unevenly matched faying surface joints or fasteners
and sharply protruding objects or corners should be
scuff sanded by hand to avoid sanding through the
paint. After sanding, you should remove the residue
with a clean, cotton cheese cloth dampened with
MIL-T-81772 thinner.
PAINT FEATHERING.—You should feather
the paint along the edge of an area that has been
chemically stripped to ensure a smooth, overlapping
transition between the old and new paint surfaces.
The smooth overlapping paint film will prevent soil
from accumulating in the junction between the old
and new paint films.
Feathering should be
accomplished with 280 or 320 grit aluminum oxide
cloth or a flap brush. The major portion of thick paint
films may be removed with an oscillating sander with
240 or finer grit aluminum oxide cloth. Do not allow
the oscillating sander to touch bare metal. The
contact between an operating sander and bare metal
will damage the metal, which, in turn, may cause
future corrosion. The oscillating sander should not be
used after first indications of primer exposure. You
should use a flap brush or hand-held 240 grit or finer
aluminum oxide cloth for final feathering operations.
TREAT AND SEAL.—Chemical conversion
treatment is an extremely important part of the
corrosion control process. Properly applied chemical
treatments impart corrosion resistance to metal. It
also improves the adhesion of the paint system. You
should use chemical conversion coating materials
according to the procedures outlined in the NA
01-1A-509.
Figure 14-29.—Flap brush with mandrel.
14-31
