Sequoia Aircraft Corporation F.8L Falco, Construction Manual

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F.8L Falco Construction Manual 9–4 Revision 4, March 1, 2002
Note that aluminum pigmented varnish is still superior to polyurethane and epoxy paints. This
does not take into account the greater life of polyurethane and epoxy coatings.
We recommend that epoxy or polyurethane coatings be used on the interior surfaces of the Falco.
In addition, we recommend that two coats be used. There are a variety of products which may be
used. Remember, it is the durability of the polyurethane and epoxy finishes which account for
their popularity. The older-style paints do a very good job of moisture-exclusion, but in time the
paints dry out and develop cracks.
We highly recommend the West System epoxies from the Gougeon Brothers, Inc. These epoxies
are specifically designed for the maximum moisture protection of wood. The West system is the
principal reason for the resurgence in popularity of wood boats. The maintenance problems long
associated with wood boats completely disappear when the West System is used. We will also be
recommending the use of West System epoxies for the exterior of the airplane. It is a wonderful
system designed specifically for protecting wood from moisture—we think it is the best available
in the world. Application instructions for West System epoxies are included in the Technical
Manual offered by Gougeon Brothers, Inc.
The West System epoxies are 100% solids systems. The epoxies are thinned with reactive
diluents—reactive means that the thinners become part of the chemical reaction and form part of
the plastic film on the wood. The use of ordinary solvents in such a finish causes a porous film to
develop since the solvent evaporate as the epoxy hardens.
Using epoxies as both wood glue and moisture-protection varnish eliminates the need for
masking; however, if you are using other glues (resorcinol, Aerolite, etc) you must still mask as
these glues will not adhere to epoxy. Only epoxy will adhere to epoxy.
Many builders use T-88 as a wood glue, and thin it with lacquer thinner and apply with a brush
for moisture protection; however the solvent will evaporate and cause a porous film. Chem-Tech
sells a low viscosity sheathing resin to protecting wood.
Stits Poly-Fiber’s EV-400 epoxy spar varnish is a clear gloss exterior varnish which may be applied
with brush or spray gun. Stits also makes a two-part urethane spar varnish, UV-550, for marine
and aircraft wood surfaces. This clear gloss interior and exterior varnish may be applied with a
brush or spray gun.
If you do not want to go to the trouble of using a two-part urethane or epoxy finish, then you
should consider the one-part urethanes. These are sold under a variety of names—Verathane is
one—and are sold by many boat yards. These are slightly better than spar varnish (see
“polyurethane varnish, one component/oil modified” in table above) but they are not as good as
the two-part finishes. The appeal of the one-part urethanes is obvious since you just grab your
brush and go to work whenever you need to.
Application Procedures
The interior surfaces of the airplane are usually inaccessible after the plywood covering has been
glued on both sides, yet the interior surfaces must be coated. Several methods have been used by
manufacturers in the past. These include various sloshing and dipping methods; for example, the
Bellanca Viking wing was given a single dip in a Glidden sealer. The methods used on production
aircraft are normally inspired more by production efficiencies than by a desire to attain the best
moisture protection.