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.