FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 2. Fabric Covering | 2. Application of Dope | 2-23. Coating Application Defects
AC 43.13-1B
9/8/98
prints, but are usually the result of improper
dope application. Pinholes are usually found
in a second layer of fabric such as finishing
tapes and reinforcing patches or over underly
ing, non-porous structures; such as leading
edges, turtle decks, and plywood surfaces.
Any non-porous structure under fabric will act
as a backstop and will resist complete dope
penetration into the fabric. Microscopic cavi
ties between the backstop and fabric collect
escaping solvent vapors during the drying pro
cess and balloon up through the surface leav
ing pinholes, or become pinholes when the top
of the balloon is sanded. Moisture, in the fab
ric or on the backstop surface, also interferes
with complete dope penetration, resulting in
pinholes. The remedy for pinholes, at any
stage before the final finish coat, is to add
blush retarder to low viscosity dope and care
fully brush over the affected surfaces to pene
trate into and fill the pinholes. Discontinue
brushing after five or six strokes to avoid
leaving brush marks.
c. Orange Peel. A rough spray gun-
applied finish, similar to the texture of an or
ange peel, may be caused by one or more of
the following conditions:
(1) Viscosity of material being sprayed
is too high.
(6) Wrong thinner used and drying too
fast.
(7) Spray gun not properly adjusted.
The spray gun should be adjusted to a uniform
spray pattern with the material atomized to de
posit fine, wet particles that merge and form a
smooth film.
d. Blisters. One or more of the following
conditions my cause blisters:
(1) Freshly coated surface placed in hot
sunlight or high temperature area to accelerate
drying time, causing the vapor from rapidly
evaporating solvents to be trapped.
(2) Excessive high air pressure used to
spray heavy coats which “blasts” air bubbles
into the coating.
(3) Water or oil in air supply.
e. Runs, Sags, and Curtains. These de
fects may be caused by one or more of the
following conditions:
(1) Viscosity of material being sprayed
is too low.
(2) Coats applied too heavily.
(2) Air temperature is too high.
(3) Spraying in direct sunlight, onto a
hot surface or in a drafty/windy condition,
which causes a fast solvent evaporation.
(3)
coats.
(4)
surface.
Insufficient drying time between
Spray gun held too close to work
(4) Spray gun, tip, cap, and/or needle
are not properly matched for the type material
being sprayed.
(5) Volume of air available from the
compressor not sufficient for spray gun.
(5) Improperly adjusted spray gun.
f. Spray Gun Laps and Streaks. These
defects may be caused by one or more of the
following conditions:
Page 2-30
Par 2-23