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