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F.8L Falco Construction Manual
9–2
Revision 4, March 1, 2002
The surface of wood is vascular and moderately absorptive of liquids. Wood surfaces, therefore,
must be rendered nonabsorptive by applying sealer or primer, which penetrates only far enough to
close the openings in the surface, before a uniform coating of finish can be spread over the surface.
Hardwood with pores as large as those in birch require wood filler applied by wiping across the
grain of the wood to plug the large pores. If a finish with a mirror-like smoothness is required,
wood of any kind usually must be coated with a sanding surfacer, part of which is sanded away
after it has dried, to yield a perfectly smooth surface for the application of the final coating.
To be durable, wood finishes must remain somewhat plastic throughout their useful life so that
they can accommodate themselves to the changes in shape and dimensions of the surface. The
required degree of plasticity usually runs counter to the desire for speed in drying and hardness of
coating; plasticity is provided by drying oils or soft resins, whereas fast drying and hardness come
from hard resins or cellulose esters.
Finishing systems when dry should add as little weight to the aircraft as is consistent with the
attainment of their primary objectives.
The most effective coating of the 1950s was aluminum enamel, followed by gloss enamels and
varnishes. Among the findings:
• Deeply penetrating finishes, such as water-repellent preservatives, afford
relatively low moisture-excluding effectiveness but may provide a significant
degree of water repellency.
• Slightly penetrating finishes that form little or no coating over the surface of the
wood, such as sealers, are lower in water repellency than the better water-
repellent preservatives when only one application is made, but a second
application often results in somewhat higher water repellency than is obtained
with water repellents, though the moisture-excluding effectiveness remains low.
The sealers are designed primarily to render the surface of wood non-absorptive
for the liquids in coating materials applied subsequently, but two or more
applications of sealer are used also as a moderately protective finish for surfaces
not exposed to the weather.
• Coatings of a porous nature, such as lusterless camouflage enamels and
camouflage lacquers, do not provide much moisture-excluding effectiveness.
• Coatings of a nonporous nature, such as spar varnish, when so applied as to form
a film of appreciable thickness (0.001” to 0.003”) over the surface of wood,
achieve reasonably high moisture-excluding effectiveness.
• Pigmented coatings of a nonporous nature, such as semigloss or gloss enamel,
have materially higher moisture-excluding effectiveness than otherwise similar
coatings without pigments.
• Aluminized coatings, which are pigmented with aluminum in the form of thin
flakes, are capable of attaining very high moisture-excluding effectiveness even
in thin coatings of light weight. For full effectiveness, however, at least one
aluminized coat should be a priming coat or an undercoat, that is, it should be
sandwiched between the wood and succeeding coats or between coats. When
Summary of Contents for F.8L Falco
Page 1: ...F 8L Falco Construction Manual...
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