another gelcoat story

"Bob Kuykendall" wrote in message
...
On Aug 26, 4:18 pm, Uncle Fuzzy wrote:

Those things give me the
willies, I'm always worried about carbon monoxide poisoning.

Thanks, Bob K.


As well you should be!

Carbon Monoxide detectors are available and inexpensive. They look like
smoke detectors.
Pilot shops sell CO detectors for the cockpit.


Insidious and deadly. Use extreme caution.

Hartley Falbaum

On Aug 26, 9:02*pm, Uncle Fuzzy wrote:
On Aug 26, 5:07*pm, Bob Kuykendall wrote:

On Aug 26, 4:18*pm, Uncle Fuzzy wrote:

Was Brad using a Space Heater, or a forced air gas furnace like you
have? I wouldn't think your heater would be a problem.

Brad laid up his fuselage shells at my shop, using my shop heater, not
a space heater. It's a Modine Hot Dawg 75 kbtu unit I put up several
years ago.

In the past I've used kerosene and propane space heaters, but mostly
just with quickie polyester/glass layups. Those things give me the
willies, I'm always worried about carbon monoxide poisoning.

Thanks, Bob K.

That's what I thought. *Unfortunately, that kinda' decreases the
chances that excess moisture in the air caused the epoxy not to bond
to the gelcoat.

The process the factories use has developed over quite some time.
Important factors include:
1) The exact chemistries of the gelcoat and epoxy being used. These
are chemically disimilar materials being asked to form a "permanent"
bond during curing.
2) The timing of the process. The time from when gelcoat is sprayed
and has gelled- but not cured- to when the first application of epoxy
is important to getting whatever "bond" you get between materials .

Using a developmental process with different materials will obviously
require a good bit of testing.

Another option could be to skip the whole gelcoat thing and do the
lamination of epoxy/glass/carbon directly in the mold and accept that
it will need pinhole/prime/fill and then paint. You would avoid the
time delay failure mode that gelcoat finishes have inherent to them.
They all fail- its only a matter of time till the gelcoat comes off in
sheets or chips.

FWIW
UH

wrote:


Another option could be to skip the whole gelcoat thing and do the
lamination of epoxy/glass/carbon directly in the mold and accept that
it will need pinhole/prime/fill and then paint. You would avoid the
time delay failure mode that gelcoat finishes have inherent to them.
They all fail- its only a matter of time till the gelcoat comes off in
sheets or chips.

It's all about the duration, though:

Time = 5 years = angry owner
Time = 50 years = happy owner(s)

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?

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Aug 27, 1:37*pm, Eric Greenwell wrote:
wrote:

Another option could be to skip the whole gelcoat thing and do the
lamination of epoxy/glass/carbon directly in the mold and accept that
it will need pinhole/prime/fill and then paint. You would avoid the
time delay failure mode that gelcoat finishes have inherent to them.
They all fail- its only a matter of time till the gelcoat comes off in
sheets or chips.

It's all about the duration, though:

Time = 5 years = angry owner
Time = 50 years = happy owner(s)

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?

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes"http://tinyurl.com/y739x4
* * * New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org

The painted gliders still come out of the mold with gelcoat. It gives
them something to sand and provide basis for finish.
Life isn't known yet because the aren't that many out there with
original PU finishes. It has only been commonly available, as far as I
know, for maybe 5 yrs. If you can keep moisture and UV away from it, I
would expect gelcoat to last quite a while, certainly longer than
"natural" gelcoat.
All this said, we have a Std Libelle in our club which is over 35 yr
old and the finish on the wings(original) is still excellent.
We also have an ASK-21 which is about 25 yr old which I expect we will
be able to take the gelcoat off with a chisel(don't ask) in chunks.

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

At 19:24 27 August 2008, wrote:
On Aug 27, 1:37=A0pm, Eric Greenwell wrote:
wrote:

Another option could be to skip the whole gelcoat thing and do the
lamination of epoxy/glass/carbon directly in the mold and accept
that
it will need pinhole/prime/fill and then paint. You would avoid the
time delay failure mode that gelcoat finishes have inherent to them.
They all fail- its only a matter of time till the gelcoat comes off
in
sheets or chips.

It's all about the duration, though:

Time =3D 5 years =3D angry owner
Time =3D 50 years =3D happy owner(s)

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?

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes"http://tinyurl.com/y739x4
=A0 =A0 * New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation"
atwww.motorglider.org

The painted gliders still come out of the mold with gelcoat. It gives
them something to sand and provide basis for finish.
Life isn't known yet because the aren't that many out there with
original PU finishes. It has only been commonly available, as far as I
know, for maybe 5 yrs. If you can keep moisture and UV away from it, I
would expect gelcoat to last quite a while, certainly longer than
"natural" gelcoat.
All this said, we have a Std Libelle in our club which is over 35 yr
old and the finish on the wings(original) is still excellent.
We also have an ASK-21 which is about 25 yr old which I expect we will
be able to take the gelcoat off with a chisel(don't ask) in chunks.
That's because the first is schwabellack gel an the second is
vorgelat(undecoat) or T35. I have 1974 Club Libelle with good original
gel. the trouble with Schwabellack is it gets very hard very quickly so is
a pain to finish. "gel coat" means that, epoxy goes on once it has gelled
, not cured. Normally epoxy and polyester are not considered compatible

having refinished more than one glider in gelcoat, i am not convinced it
bonds to cured epoxy very well, automotive paint systems may well be more
reliable.

there is some useful info on the DG website in the glider manufacturing
and optional paint finish articles. they seem to use gel as an undercoat
even if painting.

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