Dear Rebekah and others,
I have experienced the same phenomenon with epoxy.
Anyway, here's the way I understand it and have solved my problems.
My previous experience was using very small quantities as adhesive.
By "small" I mean generally mixing a tablespoon or less at a time.
Later I had occasion to mix larger quantities - by which I mean a
cup or more at a time. Then I noticed the heat problem. It is easy
to solve. Here's how it happens and how to solve it.
The chemical reaction by which the epoxy hardens produces heat. In
small applications, say mixing a wee bit on a flat surface or even
in a small container, the surface area of the mixture is relatively
large and so the heat dissipates quickly to the surrounding
environment. When you mix "large" quantities most of the mixture
is not close to the surface where it can dissipate the heat
generated by the chemical reaction. Also, because the stuff is
thick and sticky, it doesn't circulate within its container by
convection the way water would if heated. So the heat at the
center of the mass stays where it is. Finally, heat accelerates
chemical reactions, therefore the reaction proceeds ever faster as
the temperature rises thus producing more heat faster and thus
reacting faster and thus .... well I think you get the idea. Heat
will also accelerate the hardening of the mixture so your working
time is drastically reduced or even eliminated altogether.
The solution is to mix your epoxy so that it has a chance to
dissipate the heat. That might mean that instead of mixing in a deep
container, (tin can or plastic yogourt container), you might use a
pan which is wide and shallow, like a disposable aluminum pie plate
, tray, or cookie sheet or some similar container. The stuff
spreads out into a thinner layer, more surface is exposed to the
air, and heat can escape. Also the material of the container
should be conductive so that heat can easily pass out through the
walls and bottom of the container. So a metal container would be
better than plastic or glass. You can use a wide spatula-like
stirrer instead of a small stick.
One of the other people suggested varying the hardener-resin ratio.
I'm not enough of a chemist to know about that. However, in
researching the topic earlier I have learned that there are many
different kinds of "epoxy" produced for the various intended
purposes. Some of them require quite specific conditions to work as
intended; temperature, humidity, proportions of mixture etc.
Without being quite certain of the properties of the epoxy at hand,
I wouldn't mess with the proportions. It might work, or not at all.
You can check with the manufacturer for technical info.
But the heat problem can be solved as described above. Keep it cool
and mix in a way that allows heat to escape.
ALSO - Definitely do not mix in waxed cups as the heat will melt
the wax into the epoxy and wax causes no end of trouble in all sorts
ALSO - Epoxy frequently produces allergic reactions, sometimes
quite serious and dangerous. I have known people who have become
sensitized to the stuff over time so that years later they could not
walk into a room where it was being used without swelling up as
though snake-bitten. The fumes from your over-heated mixtures sound
ALSO - The "cautions" printed on the label of the hardeners about
danger to the eyes are generally understated to what I consider a
criminal degree. Someof these hardeners will produce permanent
blindness in mere seconds. Don't be careless about your eyes. There
is no first aid or second chance with the stuff.
Marty in Spring-like Victoria