Odd epoxy/gelcoat problem
 

I've done many repairs with epoxy and covered them with gelcoat, with no
problems with curing or adhesion. However, I'm having a problem on one
particular boat. I did a structural repair on a kayak with epoxy and
fiberglass cloth (nothing special about it), but for some reason, the
gelcoat didn't want to cure where it was over the epoxy (I'm using
finish gelcoat, so air exposure is not the issue). I removed it and
allowed the epoxy to cure for an extra couple of days under heat. When I
re-applied the gelcoat, ~75% of it cured fine. However, I still have
three small spots that won't cure properly where it's over the epoxy.
Where it's applied over other gelcoat, it cures fine. It's been ~2 weeks
since the initial repair was made, so I'm confident that the epoxy is
well cured. I've tried using denatured alcohol, lacquer thinner, acetone
and MEK to clean the epoxy surface, but the gelcoat still won't cure
properly in these three spots. I'm using the same products that I've
used successfully many times before.

The only clue to the problem is that the uncured gelcoat takes on a
slightly yellow-greenish cast.

Any ideas?

The Gougeon folks suggest cleaning the dreaded amine blush with amonia and
water. Have you asked the vendors of either of the prducts?


"Brian Nystrom" wrote in message
...
I've done many repairs with epoxy and covered them with gelcoat, with no
problems with curing or adhesion. However, I'm having a problem on one
particular boat. I did a structural repair on a kayak with epoxy and
fiberglass cloth (nothing special about it), but for some reason, the
gelcoat didn't want to cure where it was over the epoxy (I'm using
finish gelcoat, so air exposure is not the issue). I removed it and
allowed the epoxy to cure for an extra couple of days under heat. When I
re-applied the gelcoat, ~75% of it cured fine. However, I still have
three small spots that won't cure properly where it's over the epoxy.
Where it's applied over other gelcoat, it cures fine. It's been ~2 weeks
since the initial repair was made, so I'm confident that the epoxy is
well cured. I've tried using denatured alcohol, lacquer thinner, acetone
and MEK to clean the epoxy surface, but the gelcoat still won't cure
properly in these three spots. I'm using the same products that I've
used successfully many times before.

The only clue to the problem is that the uncured gelcoat takes on a
slightly yellow-greenish cast.

Any ideas?

Brian Nystrom wrote:
I've done many repairs with epoxy and covered them with gelcoat, with no
problems with curing or adhesion. However, I'm having a problem on one
particular boat. I did a structural repair on a kayak with epoxy and
fiberglass cloth (nothing special about it), but for some reason, the
gelcoat didn't want to cure where it was over the epoxy (I'm using
finish gelcoat, so air exposure is not the issue). I removed it and
allowed the epoxy to cure for an extra couple of days under heat. When I
re-applied the gelcoat, ~75% of it cured fine. However, I still have
three small spots that won't cure properly where it's over the epoxy.
Where it's applied over other gelcoat, it cures fine. It's been ~2 weeks
since the initial repair was made, so I'm confident that the epoxy is
well cured. I've tried using denatured alcohol, lacquer thinner, acetone
and MEK to clean the epoxy surface, but the gelcoat still won't cure
properly in these three spots. I'm using the same products that I've
used successfully many times before.

The only clue to the problem is that the uncured gelcoat takes on a
slightly yellow-greenish cast.

Any ideas?

Yes - I think you got lucky the other times. Gelcoat is NOT supposed
to cure when applied over epoxy (i.e. the conventional wisdom)!

Evan Gatehouse

Jim Conlin wrote:
The Gougeon folks suggest cleaning the dreaded amine blush with amonia and
water.

I've never noticed any blush with this epoxy. With all the scraping and
chemical cleaning I've done, it's hard to believe that there could be
anything left on the surface.

Have you asked the vendors of either of the products?

I have, but haven't received a reply yet.

Evan Gatehouse wrote:

Yes - I think you got lucky the other times. Gelcoat is NOT supposed to
cure when applied over epoxy (i.e. the conventional wisdom)!

My experience has been that the "conventional wisdom" is simply wrong
and epoxy manufacturers agree. Once epoxy cures completely, it's inert,
so it shouldn't matter what you put over it unless it specifically
reacts with the epoxy chemically. I've used this particular combination
of epoxy and gelcoat successfully many times (literally from the same
cans) and have used other epoxies with this gelcoat, so I know from
experience that it works quite well.

Something has gone wrong this time, but I can't figure out what it is.
One suggestion I've been given is contamination in the epoxy or gelcoat.
That's possible, but I'm not sure what could have contaminated it.

Brian Nystrom wrote:
Evan Gatehouse wrote:

Yes - I think you got lucky the other times. Gelcoat is NOT supposed
to cure when applied over epoxy (i.e. the conventional wisdom)!


My experience has been that the "conventional wisdom" is simply wrong
and epoxy manufacturers agree. Once epoxy cures completely, it's inert,
so it shouldn't matter what you put over it unless it specifically
reacts with the epoxy chemically. I've used this particular combination
of epoxy and gelcoat successfully many times (literally from the same
cans) and have used other epoxies with this gelcoat, so I know from
experience that it works quite well.

Something has gone wrong this time, but I can't figure out what it is.
One suggestion I've been given is contamination in the epoxy or gelcoat.
That's possible, but I'm not sure what could have contaminated it.

Is it possible that the epoxy mix was rich in one or the other of
the components, some of which permeates the epoxy, and which cannot
cure without it's required co-component?

Might adding a little of the other cause it to set up to the point
where it actually becomes "inert?"

Might it then work better with the gelcoat as you would expect?

Or would it be better to remove the epoxy, recoat it with a more
careful mix of epoxy, then finish?

If one of the epoxy components has been around for a while is it
possible it has become "corked", that is, oxodized to the point
where it is not still the epoxy part you bought? Almost everything
oxidizes over time. I have had old polyester resin gum up, it seems
to set up slowly with air, humidity, or UV, sometimes. MEK is an
oxidizer.

Have you done a subsequent test to see if this leftover old epoxy
will still set up under normal conditions?

It sounds like a contamination problem, you sure the dog didn't pee
in your mash, or summat?

Terry K

Check the expiration date on the gelcoat. It sounds like the mekp is not
curing the entire batch.
Bruce

--
Shield Finishes and Nauticoat Marine Finish Systems
www.shieldfinishes.com
"Terry Spragg" wrote in message
...
Brian Nystrom wrote:
Evan Gatehouse wrote:

Yes - I think you got lucky the other times. Gelcoat is NOT supposed to
cure when applied over epoxy (i.e. the conventional wisdom)!


My experience has been that the "conventional wisdom" is simply wrong and
epoxy manufacturers agree. Once epoxy cures completely, it's inert, so it
shouldn't matter what you put over it unless it specifically reacts with
the epoxy chemically. I've used this particular combination of epoxy and
gelcoat successfully many times (literally from the same cans) and have
used other epoxies with this gelcoat, so I know from experience that it
works quite well.

Something has gone wrong this time, but I can't figure out what it is.
One suggestion I've been given is contamination in the epoxy or gelcoat.
That's possible, but I'm not sure what could have contaminated it.

Is it possible that the epoxy mix was rich in one or the other of the
components, some of which permeates the epoxy, and which cannot cure
without it's required co-component?

Might adding a little of the other cause it to set up to the point where
it actually becomes "inert?"

Might it then work better with the gelcoat as you would expect?

Or would it be better to remove the epoxy, recoat it with a more careful
mix of epoxy, then finish?

If one of the epoxy components has been around for a while is it possible
it has become "corked", that is, oxodized to the point where it is not
still the epoxy part you bought? Almost everything oxidizes over time. I
have had old polyester resin gum up, it seems to set up slowly with air,
humidity, or UV, sometimes. MEK is an oxidizer.

Have you done a subsequent test to see if this leftover old epoxy will
still set up under normal conditions?

It sounds like a contamination problem, you sure the dog didn't pee in
your mash, or summat?

Terry K

Terry Spragg wrote:
Brian Nystrom wrote:

Evan Gatehouse wrote:

Yes - I think you got lucky the other times. Gelcoat is NOT supposed
to cure when applied over epoxy (i.e. the conventional wisdom)!



My experience has been that the "conventional wisdom" is simply wrong
and epoxy manufacturers agree. Once epoxy cures completely, it's
inert, so it shouldn't matter what you put over it unless it
specifically reacts with the epoxy chemically. I've used this
particular combination of epoxy and gelcoat successfully many times
(literally from the same cans) and have used other epoxies with this
gelcoat, so I know from experience that it works quite well.

Something has gone wrong this time, but I can't figure out what it is.
One suggestion I've been given is contamination in the epoxy or
gelcoat. That's possible, but I'm not sure what could have
contaminated it.


Is it possible that the epoxy mix was rich in one or the other of the
components, some of which permeates the epoxy, and which cannot cure
without it's required co-component?

Might adding a little of the other cause it to set up to the point where
it actually becomes "inert?"

Might it then work better with the gelcoat as you would expect?

Or would it be better to remove the epoxy, recoat it with a more careful
mix of epoxy, then finish?

If one of the epoxy components has been around for a while is it
possible it has become "corked", that is, oxodized to the point where it
is not still the epoxy part you bought? Almost everything oxidizes over
time. I have had old polyester resin gum up, it seems to set up slowly
with air, humidity, or UV, sometimes. MEK is an oxidizer.

Have you done a subsequent test to see if this leftover old epoxy will
still set up under normal conditions?

The epoxy was carefully mixed (it's a 1: 1 ratio, so it's hard to screw
up) and it set up just fine, so I don't think there's anything wrong
with it in that regard.

It sounds like a contamination problem, you sure the dog didn't pee in
your mash, or summat?

I transfer the epoxy from the original cans into catchup bottles for
easier handling when mixing small batches. The stuff I used for the
repairs has been in those bottles for a few months. Although I can't
think of anything that could have contaminated it, it's a possibility.

Bruce on horizon wrote:
Check the expiration date on the gelcoat. It sounds like the mekp is not
curing the entire batch.

The odd thing is that it cures fine wherever it's over other gelcoat. I
have had this can for a while, so it could possibly be age related. I
could try another tube of MEKP, as I have a couple that haven't been
opened. I'll give that a shot tonight.