FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 1. Wood Structure | 1. Materials and Practices | 1-9. Bonding Temperature
AC 43.13-1B
9/8/98
surfaces. Sanding should never be continued
to the extent that it alters the flatness of the
surface. Very light sanding may also improve
the wetting of the adhesive to very hard or
resinous materials.
b. Wetting tests are useful as a means of
detecting the presence of wax, old adhesive,
and finish. A drop of water placed on a sur-
face that is difficult to wet and thus difficult to
bond will not spread or wet the wood rapidly
(in seconds or minutes). The surface may be
difficult to wet due to the presence of wax, ex-
posure of the surface to heat and pressure as in
the manufacture of hot press bonded plywood,
the presence of synthetic resins or wood ex-
tractives, or simply chemical or physical
changes in the wood surface with time. Good
wettability is only an indication that a surface
can be bonded satisfactorily. After performing
wetting tests, allow adequate time for wood to
dry before bonding. Preliminary bonding tests
and tests for bond strength are the only posi-
tive means of actually determining the bonding
characteristics of the adhesive and material
combinations. (See paragraph 1-29h.)
1-7. APPLYING THE ADHESIVE. To
make a satisfactory bonded joint, spread the
adhesive in a thin, even layer on both surfaces
to be joined. It is recommended that a clean
brush be used and care taken to see that all sur-
faces are covered. Spreading of adhesive on
only one of the two surfaces is not recom-
mended. Be sure to read and follow the adhe-
sive manufacturer’s application instructions.
1-8. ASSEMBLY TIME IN BONDING.
Resorcinol, epoxy, and other adhesives cure as
a result of a chemical reaction. Time is an im-
portant consideration in the bonding process.
Specific time constraints are as follows:
a. Pot life is the usable life of the adhesive
from the time that it is mixed until it must be
spread onto the wood surface. Once pot life
has expired, the remaining adhesive must be
discarded. Do not add thinning agents to the
adhesive to extend the life of the batch.
b. Open assembly time is the period from
the moment the adhesive is spread until the
parts are clamped together. Where surfaces
are coated and exposed freely to the air, some
adhesives experience a much more rapid
change in consistency than when the parts are
laid together as soon as the spreading has been
completed.
c. Closed assembly time is the period
from the moment that the structure parts are
placed together until clamping pressure is ap-
plied. The consistency of the adhesive does
not change as rapidly when the parts are laid
together.
d. Pressing (or clamping) time is the pe-
riod during which the parts are pressed tightly
together and the adhesive cures. The pressing
time must be sufficient to ensure that joint
strength is adequate before handling or ma-
chining the bonded structure.
NOTE: Follow the adhesive manufac-
turer’s instructions for all time limits
in the bonding process. If the recom-
mended open or closed assembly peri-
ods are exceeded, the bond process
should not be continued. Discard the
parts if feasible. If the parts cannot be
discarded, remove the partially cured
adhesive and clean the bond line per
adhesive manufacturer’s instructions
before application of new adhesive.
1-9. BONDING TEMPERATURE. Tem-
perature of the bond line affects the cure rate
of the adhesive. Some adhesive types, such as
resorcinol, require a minimum temperature
which must be maintained throughout the
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