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 | 1-6. Preparation of Wood Surfaces for Bonding
9/8/98
AC 43.13-1B
(6) Epoxy adhesives are a two-part
synthetic resin product, and are acceptable
providing they meet the requirements of para-
graph 1-4a. Many new epoxy resin systems
appear to have excellent working properties.
They have been found to be much less critical
of joint quality and clamping pressure. They
penetrate well into wood and plywood. How-
ever, joint durability in the presence of ele-
vated temperature or moisture is inadequate in
many epoxies. The epoxy adhesives generally
consist of a resin and a hardener that are mixed
together in the proportions specified by the
manufacturer. Depending on the type of ep-
oxy, pot life may vary from a few minutes to
an hour. Cure times vary between products.
CAUTION: Some epoxies may have
unacceptable thermal or other hidden
characteristics not obvious in a shop
test. It is essential that only those
products meeting the requirements of
paragraph 1-4a be used in aircraft re-
pair. Do not vary the resin-to-
hardener ratio in an attempt to alter
the cure time. Strength, thermal, and
chemical resistance will be adversely
affected. Read and observe material
safety data. Be sure to follow the ad-
hesive manufacturer’s instructions re-
garding mixing, open and closed cur-
ing time, and usable temperature
ranges.
a. Properly prepared wood surfaces.
b. Adhesive of good quality, properly
prepared, and properly selected for the task at
hand.
c. Good bonding technique, consistent
with the adhesive manufacturer’s instructions
for the specific application.
1-6. PREPARATION OF WOOD SUR-
FACES FOR BONDING. It is recommended
that no more time than necessary be permitted
to elapse between final surfacing and bonding.
Keep prepared surfaces covered with a clean
plastic sheet or other material to maintain
cleanliness prior to the bonding operation.
The mating surfaces should be machined
smooth and true with planers, joiners, or spe-
cial miter saws. Planer marks, chipped or
loosened grain, and other surface irregularities
are not permitted. Sandpaper must never be
used to smooth softwood surfaces that are to
be bonded. Sawn surfaces must approach
well-planed surfaces in uniformity, smooth-
ness, and freedom from crushed fibers. It is
advisable to clean both joint surfaces with a
vacuum cleaner just prior to adhesive applica-
tion. Wood surfaces ready for bonding must
be free from oil, wax, varnish, shellac, lacquer,
enamel, dope, sealers, paint, dust, dirt, adhe-
sive, crayon marks, and other extraneous mate-
rials.
1-5. BONDING PRECAUTIONS. Satis-
factory bond joints in aircraft will develop the
full strength of wood under all conditions of
stress. To produce this result, the bonding op-
eration must be carefully controlled to obtain a
continuous thin and uniform film of solid ad-
hesive in the joint with adequate adhesion and
penetration to both surfaces of the wood.
Some of the more important conditions in-
volve:
a. Roughening smooth, well-planed sur-
faces of normal wood before bonding is not
recommended. Such treatment of well-planed
wood surfaces may result in local irregularities
and objectionable rounding of edges. When
surfaces cannot be freshly machined before
bonding, such as plywood or inaccessible
members, very slight sanding of the surface
with a fine grit such as 220, greatly improves
penetration by the adhesive of aged or polished
Par 1-4
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