another gelcoat story

When we made my fuselage, it was winter and we were heating the shop
with a propane heater. Propane releases moisture during combustion.

So........molds are waxed multiple times, gelcoat (shurfab polyester
product) is sprayed into the mold, we leave the heater on and go home
for the night............gelcoat cures.

Next day come back to the shop, make up a batch of epoxy and a bit of
micro as the first layer against the gelcoat and then start laying in
the carbon, no veil cloth, the idea was the epoxy/micro slurry would
help reduce print thru.

Fast forward 2 years.............fuselage is now in my shop where I
have been working on the interior bits this spring/summer. I am bored
and decide to sand the fuselage with 220 then down to 320 to get ready
for top coating with Prestec. Wow.............it looks great.

I blow off the dust with a compressor and then wipe the fuselage with
a damp rag and go watch TV for a bit. A few hours later I go into the
shop and am horrified to see large areas of blisters have formed under
the gelcoat...........I am able to peel the gelcoat off in places with
my fingernail! Further investigation with a sanding block and 70 grit
paper confirm there is no secure bond between the gelcoat and the
epxoy slurry in enough areas that I resign myself to remove the
gelcoat off the entire fuselage, down to the carbon.

1/2 is already done and I'll start today on the other
half...................ugh........

so.....my theory: the gelcoat had moisture on it when we started
brushing in the epoxy...........and probably there was a temperature
issue as well that may have prevented a full cure of the epoxy/gelcoat
interface.

Anyways.............a lot of work for sure.

Next step...................get some Prestec 2481 and brush it on and
start sanding again. Gotta do this before the WX turns here in
Washington and we start the rainy season.

Brad

Next step...................get some Prestec 2481 and brush it on and
start sanding again. Gotta do this before the WX turns here in
Washington and we start the rainy season.

Brad


Bad luck with the gelcoat Brad, I would sand everything down with 80
grit, Prime with PCL Polyprimer (907 white), then sand with 220 and
spray on acrylic urethane (PPG concept super white), 4 flow coats then
block sand after 18 to 24 hrs with 600w, then 800w use dye-coat, then
let it cure for 3 days before buffing it out with liquid buffing
compound and a wool pad turning at about 1700 rpm. Gel coat was never
intended for airplanes, urethane was/is!
JJ
PS, do it before you need propane heat!

A buddy of mine had this problem while painting his Skyhawk one
winter. Our theory was that the diesel powered heater was
contaminating the air with some greasy byproduct of combustion. Two
days after painting the paint was flaking off like a bad sunburn.
Since then I have kept heaters away from paint projects.

Brad – There are several issues that are potential problems: As has
been pointed out there could be a moisture issue, or a moisture +
combustion by-product contamination problem. Another contributor to
gel coat adhesion is the timing of the cure and laminate application.
It is not recommended to allow gel coat to cure overnight before
applying the laminate. The window for maximum adhesion (with properly
cured gel coat) is 45-minutes to 3-hours. If the temp was high enough
during the overnight period, the advanced state-of-cure of the gel
coat may have resulted in a less than optimum interface bond. The last
potential concern is the use of micro (or any other filler) in the
resin. This reduces the wetting capability of the resin and again
reduces the interface bond strength. I’m guessing you had all these
factors leaning in the wrong direction.

Bob

thanks for the comments and suggestions guys. as to the amount of gas
we burned that night, Bob K might know, it was in his shop where we
layed up the skins.............

I am leaning now towards JJ's suggestion and not go with the Prestec.
I have pretty crude painting facilities at my shop (read none) so I
hope the PPG products can tolerate a less than ideal spraying
environment.

when I sanded down the second fuselage half, I noticed that the
gelcoat on that side was a bit more tenacious that the first side,
sorta had me wondering if I could leave some on and just prime over
it, but despite have sore arms, I bit the bullet and sanded it all
off..............well, that's the plan, there is still alittle bit
left to do.

my hat is off to all those brave folks who have done
this..............it is not fun!

Brad

PS............Bob L..........we are going to make some wings in the
next month or so at Bob's shop...........what can we do to prevent
another disaster like this!!!

On Aug 24, 5:30*pm, RL wrote:
Brad – There are several issues that are potential problems: *As has
been pointed out there could be a moisture issue, or a moisture +
combustion by-product contamination problem. Another contributor to
gel coat adhesion is the timing of the cure and laminate application.
It is not recommended to allow gel coat to cure overnight before
applying the laminate. The window for maximum adhesion (with properly
cured gel coat) is 45-minutes to 3-hours. If the temp was high enough
during the overnight period, the advanced state-of-cure of the gel
coat may have resulted in a less than optimum interface bond. The last
potential concern is the use of micro (or any other filler) in the
resin. This reduces the wetting capability of the resin and again
reduces the interface bond strength. I’m guessing you had all these
factors leaning in the wrong direction.

Bob

I'm a newbie at painting and refinishing. I used the products mentioned
and got a good job in my garage. The biggest problem I had was sanding
through the edges while polishing it out. Put LOTS of paint on the leading
edges and any corners or sharp compound curves and sand very, very lightly
there. The PPG products are vary easy to deal with and seem to hold up
well. While you are at the paint store, ask them about 3M "Guide Coat".
This product is a real time saver and one $25 container can do several
ships.

Brian
At 02:20 25 August 2008, Brad wrote:
thanks for the comments and suggestions guys. as to the amount of gas
we burned that night, Bob K might know, it was in his shop where we
layed up the skins.............

I am leaning now towards JJ's suggestion and not go with the Prestec.
I have pretty crude painting facilities at my shop (read none) so I
hope the PPG products can tolerate a less than ideal spraying
environment.

when I sanded down the second fuselage half, I noticed that the
gelcoat on that side was a bit more tenacious that the first side,
sorta had me wondering if I could leave some on and just prime over
it, but despite have sore arms, I bit the bullet and sanded it all
off..............well, that's the plan, there is still alittle bit
left to do.

my hat is off to all those brave folks who have done
this..............it is not fun!

Brad

When you say 'less than ideal', the main thing is air flow to get the fumes
out and keeping the outside dust from getting in. I have sprayed in very
humid weather here in the Houston area. We used Ful-Thane 2K Urethane with
their primer.

"Brian Bange" wrote in message
...
I'm a newbie at painting and refinishing. I used the products mentioned
and got a good job in my garage. The biggest problem I had was sanding
through the edges while polishing it out. Put LOTS of paint on the leading
edges and any corners or sharp compound curves and sand very, very lightly
there. The PPG products are vary easy to deal with and seem to hold up
well. While you are at the paint store, ask them about 3M "Guide Coat".
This product is a real time saver and one $25 container can do several
ships.

Brian
At 02:20 25 August 2008, Brad wrote:
thanks for the comments and suggestions guys. as to the amount of gas
we burned that night, Bob K might know, it was in his shop where we
layed up the skins.............

I am leaning now towards JJ's suggestion and not go with the Prestec.
I have pretty crude painting facilities at my shop (read none) so I
hope the PPG products can tolerate a less than ideal spraying
environment.

when I sanded down the second fuselage half, I noticed that the
gelcoat on that side was a bit more tenacious that the first side,
sorta had me wondering if I could leave some on and just prime over
it, but despite have sore arms, I bit the bullet and sanded it all
off..............well, that's the plan, there is still alittle bit
left to do.

my hat is off to all those brave folks who have done
this..............it is not fun!

Brad

Brad, I wouldn't brush on the primer, half your sanding will be to
just remove the brush marks. You can get a cheap gun and compressor
for this. It is usually best to use the primer that is recommended by
the paint you are using, but most are gray in color and this will
start to show through if (when) you get a little to heavy handed with
the wet sanding during the finishing process. That is why I use PCL
Polyprimer, because it is pure white and believe me white is the way
to go. You do need good ventilation any time your spraying anything,
not only to prevent trapping unwanted by-products in the paint, but
you don't want to be trapping any of this stuff in your lungs, either!
That is REALLY true when using uretahne, we had a mechanic here who
recovered a Cub in the dead of winter with propane heaters running
inside the shop. He didn't want to ventilate because he would lose all
his heat. Then he sprayed urethane in the same environment (probably
with just a dust mask)........................anyway, he is no longer
with us!
From personal experience, I was spraying uerthane one evening and
started to lose my peripheral vision, then I tightened up the mask and
got it back! Scary stuff, I could have passed out, alone inside a
paint booth full of stuff that can kill you. I use a resporator now,
not too expensive, $300'ish from Spruce and Specialty.
Oh, my how I have carried on and we haven't even touched on the
biggest proplem you will face. Pumping water droplets out of your
spray gun. Got to go wet sand yesterdays paint.............
JJ

On Aug 25, 10:24 am, JJ Sinclair wrote:
Brad, I wouldn't brush on the primer, half your sanding will be to
just remove the brush marks. You can get a cheap gun and compressor
for this. It is usually best to use the primer that is recommended by
the paint you are using, but most are gray in color and this will
start to show through if (when) you get a little to heavy handed with
the wet sanding during the finishing process. That is why I use PCL
Polyprimer, because it is pure white and believe me white is the way
to go. You do need good ventilation any time your spraying anything,
not only to prevent trapping unwanted by-products in the paint, but
you don't want to be trapping any of this stuff in your lungs, either!
That is REALLY true when using uretahne, we had a mechanic here who
recovered a Cub in the dead of winter with propane heaters running
inside the shop. He didn't want to ventilate because he would lose all
his heat. Then he sprayed urethane in the same environment (probably
with just a dust mask)........................anyway, he is no longer
with us!
From personal experience, I was spraying uerthane one evening and
started to lose my peripheral vision, then I tightened up the mask and
got it back! Scary stuff, I could have passed out, alone inside a
paint booth full of stuff that can kill you. I use a resporator now,
not too expensive, $300'ish from Spruce and Specialty.
Oh, my how I have carried on and we haven't even touched on the
biggest proplem you will face. Pumping water droplets out of your
spray gun. Got to go wet sand yesterdays paint.............
JJ

My $0.02 on iso-cyanates and urethane paint:

Back around 1990 I painted a ship with Deltron Acrylic Urethane (PPG).
The results were great... However, I will not be doing that again.
Urethanes are simply too toxic for this amateur. Iso-cyanates are
incredibly bad news. How bad? To give an idea: I walked back into my
"booth" without protection about an hour after spraying the fill coat
(K-201 iirc) on one wing and almost instantly had bronchial
constriction and a really nasty head buzz. No more than 60 seconds
exposure an hour after spraying.... Scared the hell out of me. If
you must do this... at least be aware of who is down wind and how
far. If you decide to cheap out and forge ahead with a carbon filter
mask instead of a proper air-supply system, change the filters
frequently and don't wait for odor to become noticeable through the
mask, cause you'll be sorry. Furthermore, wear the mask any -- I mean
*any* -- time the paint is open including mixing.

Take the warnings seriously.

Today's mad hatter is more likely to be an auto body guy. Doubt me?
Go hang at the local body shop and see what you see. There's no way
to do this stuff with zero exposure.

I have a very lightly used Graco HVLP spray system that I'd be willing to
sell. It eliminates oils and moisture introduced by a compressor. It is
complete with mask to deliver fresh, outside air under positive pressure
to the wearer. Write privately for details.


At 15:13 25 August 2008, PMSC Member wrote:
On Aug 25, 10:24 am, JJ Sinclair wrote:
Brad, I wouldn't brush on the primer, half your sanding will be to
just remove the brush marks. You can get a cheap gun and compressor
for this. It is usually best to use the primer that is recommended by
the paint you are using, but most are gray in color and this will
start to show through if (when) you get a little to heavy handed with
the wet sanding during the finishing process. That is why I use PCL
Polyprimer, because it is pure white and believe me white is the way
to go. You do need good ventilation any time your spraying anything,
not only to prevent trapping unwanted by-products in the paint, but
you don't want to be trapping any of this stuff in your lungs,
either!
That is REALLY true when using uretahne, we had a mechanic here who
recovered a Cub in the dead of winter with propane heaters running
inside the shop. He didn't want to ventilate because he would lose
all
his heat. Then he sprayed urethane in the same environment (probably
with just a dust mask)........................anyway, he is no longer
with us!
From personal experience, I was spraying uerthane one evening and
started to lose my peripheral vision, then I tightened up the mask and
got it back! Scary stuff, I could have passed out, alone inside a
paint booth full of stuff that can kill you. I use a resporator now,
not too expensive, $300'ish from Spruce and Specialty.
Oh, my how I have carried on and we haven't even touched on the
biggest proplem you will face. Pumping water droplets out of your
spray gun. Got to go wet sand yesterdays paint.............
JJ

My $0.02 on iso-cyanates and urethane paint:

Back around 1990 I painted a ship with Deltron Acrylic Urethane (PPG).
The results were great... However, I will not be doing that again.
Urethanes are simply too toxic for this amateur. Iso-cyanates are
incredibly bad news. How bad? To give an idea: I walked back into my
"booth" without protection about an hour after spraying the fill coat
(K-201 iirc) on one wing and almost instantly had bronchial
constriction and a really nasty head buzz. No more than 60 seconds
exposure an hour after spraying.... Scared the hell out of me. If
you must do this... at least be aware of who is down wind and how
far. If you decide to cheap out and forge ahead with a carbon filter
mask instead of a proper air-supply system, change the filters
frequently and don't wait for odor to become noticeable through the
mask, cause you'll be sorry. Furthermore, wear the mask any -- I mean
*any* -- time the paint is open including mixing.

Take the warnings seriously.

Today's mad hatter is more likely to be an auto body guy. Doubt me?
Go hang at the local body shop and see what you see. There's no way
to do this stuff with zero exposure.