Refinishing gelcoat

In article ,
says...
It struck me the other day that the materials used to cover R/C models these
days could be used to 'refinish' ships on which the gelcoat had
deteriorated. We are already 'happy' to stick .5m wide pieces of orange tape
to the surfaces of gliders and do so with impunity.

Solarfilm ( a trade name ) can be obtained in 10m long rolls up to .7m
wide. I'm fairly certain that a roll would do the upper surface of a 15m
ships wing. If the wing was lightly sanded first to remove any raised edges
of the cracked gelcoat and to restore the profile, the material could be
laminated to the wing leaving an incredibly slick finish. These materials
are surprisingly srong and an entire roll weighs very little.

I've had some Monokote (Solarfilm equivalent) and a wing tip sitting
on my bench for several months now, planning to experiment with
covering up small dents in wings, bridging the depression caused by a
shrinking spar, and just adding some decoration. Ian's posting
motivated me to actually try sticking a few pieces on to the wing tip
(left over from fitting winglets).

It's going to take some practice to get it on smoothly, I can see.
Part of the problem is the temperature required to activate the
adhesive (instructions say to set the iron at 275 F), which is well
above the epoxy limit. Another problem is avoiding air bubbles when
covering large areas. I'm sure these can be dealt with.

The biggest problem I can see is ensuring that the covering doesn't
peel up in flight, perhaps rendering an aileron or elevator unusable.
Determining the effects of long term exposure (longer than a year,
say) will be important, as gliders typically spend far more time
outdoors than model airplanes, so their experience might not be a good
guide. What will sunlight, desert temperatures and wave flight chills
do to the material when applied over fiberglass or carbon structures?

Even if you convince yourself it's safe and sane, regulatory and
insurance issues need to be dealt with. In the US, a covering on the
flying surfaces might need an FAA approval, and I'd like to be there
when the first pilot goes to the insurance company and explains how he
is going to cover his glider with a plastic sheet, wants to know how
that might affect his coverage.

So, maybe someone with some wrecked wing parts lying around can try
the idea, and set the panels outside for exposure testing. Flight
testing with a full chord, 10 inch wide strip of white material near
the wing root probably wouldn't be hazardous, even if the strip
peeled. Ditto for pieces on the turtle deck. Or maybe on a spoiler cap
- if it peels up and acts like a small spoiler, it's in the right
place!

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Eric Greenwell
Richland, WA (USA)

"Eric Greenwell" wrote in message
.. .

...................
It's going to take some practice to get it on smoothly, I can see.
Part of the problem is the temperature required to activate the
adhesive (instructions say to set the iron at 275 F), which is well
above the epoxy limit. Another problem is avoiding air bubbles when
covering large areas. I'm sure these can be dealt with.

The biggest problem I can see is ensuring that the covering doesn't
peel up in flight, perhaps rendering an aileron or elevator unusable.
Determining the effects of long term exposure (longer than a year,
say) will be important, as gliders typically spend far more time
outdoors than model airplanes, so their experience might not be a good
guide. What will sunlight, desert temperatures and wave flight chills
do to the material when applied over fiberglass or carbon structures?

Eric Greenwell
Richland, WA (USA)

To answer some of your questions, I used such material on my Discus back in
1985. It was still intact when I sold it 16 years later.

First, rather than Monokote, use Econokote. Made by the same company but
requires a much lower temperature for application. Econokote (vice
Monokote) is recommended for covering over solid surfaces. Also, Econokote
is more easily stretched around curves. Solarfilm also has a lower
application temperature. With Monokote, the required bonding temperature
heats up the surface (Fiberglas wing in this case). The wing, which has
mass, holds the heat which results in many bubbles of the film. The lower
temp film is much less susceptible to bubbling. If a small bubble does
occur, you can puncture it with a pin and iron it smooth.

There is no real need to worry about the heat damaging the wing. The iron
should not be held in contact long enough to really heat the wing. Due to
the difference in mass of the film and the wing surface the film is heated
to the proper temp before the wing surface gets too hot.

What I used the film for was to make an "omega" seal in the aileron gap.
One side of a strip of film (about 1/2 inch wide) was ironed to the wing,
then looped into the gap, and about 1/2 inch of the other side ironed to the
aileron. Of course the strip of film was the length of the aileron. After
16 years there was no tendency to peel. I did this on the bottom of the
wing, no sun. However, I have not seen any bad effect on models that have
been in the sun for extended periods. Also, I did only small (two1/2 inch
wide) strips. Ironing the film on a large area (complete wing) would be
much, much more difficult to control bubbling and wrinkles. The film does
shrink with temp, however, when it is heated the adhesive is also heated
(and melts) and sticks to whatever it touches. Therefore, when doing a
large surface, it is difficult to heat the film without it touching the
surface that is being covered. Not impossible, just difficult.

Duane