another gelcoat story

Do the factories offering polyurethane paint as an option to gel coat
still use a thin layer gel coat? How much does that method extend the
life of the gel coat?

Yes, it is necessary to use gel coat or an in-mold primer gel coat. As
Hank mentioned it is not practical to laminate directly on the mold
surface. The laminate will be full of pinholes and require extensive
post-mold priming and sanding before a finish coating can be applied.
Now here's a catch 22 - It is not feasible to apply a "thin" layer of
polyester gel coat. The normally recommended wet film thickness ranges
from a low of 14 mils (mil =.001") to 18+ mils. With anything thinner
than 14 mils the proportional amount of styrene lost through
evaporation becomes so high that there is not enough styrene left for
complete crosslinking. Bottomline - overly thin gel coat will be
permanently under-cured regardless of catalyst level or curing
temperature.

A linear urethane topcoat will extend the life of a well applied gel
coat substrate condsiderably.

Bob

On Aug 27, 1:31*pm, RL wrote:
Do the factories offering polyurethane paint as an option to gel coat
still use a thin layer gel coat? How much does that method extend the
life of the gel coat?

Yes, it is necessary to use gel coat or an in-mold primer gel coat. As
Hank mentioned it is not practical to laminate directly on the mold
surface. The laminate will be full of pinholes and require extensive
post-mold priming and sanding before a finish coating can be applied.
Now here's a catch 22 - It is not feasible to apply a "thin" layer of
polyester gel coat. The normally recommended wet film thickness ranges
from a low of 14 mils (mil =.001") to 18+ mils. With anything thinner
than 14 mils the proportional amount of styrene lost through
evaporation becomes so high that there is not enough styrene left for
complete crosslinking. Bottomline - overly thin gel coat will be
permanently under-cured regardless of catalyst level or curing
temperature.

A linear urethane topcoat will extend the life of a well applied gel
coat substrate condsiderably.

Bob


http://www.dg-flugzeugbau.de/gelcoat-e.html
http://www.dg-flugzeugbau.de/pur-lack-e.html

With anything thinner
than 14 mils the proportional amount of styrene lost through
evaporation becomes so high that there is not enough styrene left for
complete crosslinking. Bottomline - overly thin gel coat will be
permanently under-cured regardless of catalyst level or curing
temperature.


Bob,

You just solved my gelcoat problem. The layer was to thin. In the
areas where it was thicker, I had to use a DA to get it off,
everywhere else, it flaked off with the sandpaper or by sliding a
putty knife under the paint and removing "leaves" of it.

I have had ISP problems the last several days, hence my dissapearance
on this thread!

Will give you a call tonight Bob.

Brad

I believe AMS-Fligth in Slovenia is building gliders with only PU. They
have developed a method for spraying the PU in the mold prior to layup so
that the pieces comeout with a PU finish. This is the way my APIS was
built. The finish is all PU, no gelcoat that I am aware of.

http://www.ams-flight.si/ abour 1/3 of the way down the
page "AMS Sets The Standard In Glider Finishes".

John Scott

On Aug 27, 4:33*pm, "John Scott" wrote:
I believe AMS-Fligth in Slovenia is building gliders with only PU. *They
have developed a method for spraying the PU in the mold prior to layup so
that the pieces comeout with a PU finish. *This is the way my APIS was
built. *The finish is all PU, no gelcoat that I am aware of.

* * * * * *http://www.ams-flight.si/* * * *abour 1/3 of the way down the
page "AMS Sets The Standard In Glider Finishes".

John Scott

My Apis was built by Albastar, not sure what they used as a mold coat.
Whatever it was, it was really thin, and I used it as a primer coat
for Prestec 2781.

Brad