Hi -
A friend is restoring a Cessna 172 airplane, and decided to do his own
painting. I helped in matters of advising re: equipment and interpreting
instructions, and so on. He's pretty well satisfied with the results
(using Martin Senour automotive acrylic enamel) so far, but there are three
questions that mightier minds than mine could help out on:
1) When the instructions say "thin" coats, what do they mean? After one
thin coat on bare aluminum, should the aluminum still shine through, or is
that too thin?
2) He has used the proper amount of the proper reducer, but no hardener
mixed into the paint. What would be (have been) the advantages of doing
so? Of using a top coat of hardener? [A subquestion, out of curiosity:
Reading between the lines of the instructions on a can of laquer thinner he
bought for cleaning the equipment, one gets the following impression - that
laquer thinner is meant for thinning laquer (reasonably enough) and that
other paints have other reducers, and you should use them, but if you did
use this laquer thinner for thinning them, it would be like a medium speed
reducer made for middle range temperatures. Could he really have saved $15
a gallon by going this route?]
3) The big one - the first coat, conscientiously applied, dries to a high
sheen (but, if thin, isn't enough coverage). Subsequent coats suffer from
a dulling - it appears at the edges of the path of the spray and looks like
paint that was too dry when it contacted the surface. (The first coat does
this as well, but subsequent passes add to this "overspray" and it
liquifies and forms a solid coat. Second coats don't seem to work this
way.) When we did the vertical stabilizer, this wasn't a problem since the
area to be painted was relatively small. But on the wings, these dull area
never could be painted out, presumably because of the drying that takes
place before you get back to the place you started. If he paints parallel
to the leading edge of the wing, The result is zebra-like: alternating
lines of shiny and dull paint. I suspect that rubbing compound might be of
benefit, but he doesn't want to hear that. Would different thinning on
second coats improve things? Or changes in other parameters?
(We are using 55 lbs. of air pressure, per spec. Three light coats are
called for with ~15 minutes drying time between coats; increasing this time
has no noticeable effect on the problem. Changing the spray pattern to
circular reduces the size of the stripes, but they're still there. The
quantity of paint is adjusted to be just shy of the amount that would cause
running givn the usual speed at which he moves the gun - doesn't sound
"thin" to me, but he's impatient about some things.)
Any advice will be gratefully accepted and passed on.
Louis Smogor
paradox@depauw.edu
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