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
9/8/98
AC 43.13-1B
deterioration with fabric at least equal to that
used by the original manufacturer. If the qual
ity is not known, intermediate-grade fabric,
meeting TSO-C14b specification, is accept
able. Fabric may be installed in sections with
a 1/2 inch edge overlap without covering the
overlap with finishing tape. Fabric may also
be installed with the edges butted together, and
the seam covered with a minimum 1-inch wide
finishing tape. The seams may be oriented in
any direction, in reference to the line of flight.
However, overlapped seams, not covered with
a finishing tape, should be oriented rearward.
Fabric should be wrapped completely around a
wing’s leading and trailing edges and other
components, where possible, to provide fabric
to-fabric continuity around all edges to avoid a
poorly-bonded fabric edge from peeling from
the plywood surface causing serious aerody
namic consequences.
a. After the plywood surface is pre-
pared, and the two pre-coats of clear dope
have dried as recommended in para
graph 2-6 g, the fabric is pulled snug and
bonded with clear dope around the perimeter
of the fabric section. The fabric is then wetted
with distilled water to remove fold creases, in
the same manner described for fabric panel ar
eas. After the water has evaporated, a heavy
coat of low-viscosity clear dope is brushed
firmly through the fabric to soften the under
lying dope pre-coat, insuring a good bond.
Brushing techniques should be accomplished
by moving the brush from one side across to
the opposite side to remove all air bubbles and
thoroughly saturate the fabric. This is indi
cated by the plywood grain being easily visible
through the translucent fabric. Except for very
small imperfections or small dents in the ply
wood surface, voids are not permissible be
tween the fabric and plywood surfaces. Voids
may allow the fabric to balloon from the ply
wood surface, creating adverse handling char
acteristics.
b. After the first dope coat has dried at
least 1 hour at 70 °F, a second heavy coat of
clear dope is applied by brush to fill the fabric
weave and prevent pinholes. The installation
of finish tape around the perimeter of the ply
wood surfaces, leading edges, and other wear
points, is optional but recommended for wear
and chafe protection. The application of alu
minum-pigmented dope coating, sanding, and
finish coats will be the same as that specified
for fabric panel areas. Reinforcement grom
mets are not required on drain holes through
plywood surfaces.
2-23. COAT-
ING APPLICATION DEFECTS.
a. Blushing. The appearance of light
shaded dull areas on the surface as dope dries
is the result of moisture in the atmosphere
condensing on a surface due to the cooling ef
fect of the fast-evaporating components of
dope thinner escaping from the coating.
Blushing can occur at any temperature when
the humidity is above 65 percent. There are
several ways to remedy this problem. The
drying time may be slowed by adding up to
1 quart of blush retarder to 1 gallon of dope or
by increasing the temperature of the dope room
and eliminating any cooling draft from blow
ing across the surface. Blushed surfaces may
be reworked by spraying several, closely-timed
coats of a 50/50 blend of blush retarder and
dope thinner to soften and return the dope sur
face to the original liquid state. Blush retarder,
mixed with dope, may delay the full drying
time by several days, but will eventually es
cape from the dope film if the room tempera
ture is maintained an average of 70 °F.
b. Pinholes. Voids between the fabric
threads that are not filled with the first coats of
dope are called pinholes. They may be caused
by fabric contamination, such as oil or finger
Par 2-22
Page 2-29