Epoxy Fun

[Farrell]

If I am going to use a large batch of epoxy very quickly, I will just mix
into a normal container. But if I might be slow about using up the mixture,
I take a hunk of plywood and lay a piece of thick plastic over it and mix
the epoxy on the flat plastic surface. The plywood allows me to move the
mixture around. Keeping a large blob of epoxy spread thin will discourage
the heating process and you will get a lot longer pot - er, a, flat
surface - life.

Also, West System has #209 hardener which has double the pot life of 206.

Terry Farrell


> List,
>
> I had an interesting experience with epoxy the other day, so I thought I'd
> post my situation as well as the response from West System.  It helped me
> and may help others who are not as familiar with the use of epoxy.
>
> Just started working on some finger worn keys, following the method posted
> by Ed Foote some time back.  Basically it involves using West System A
group
> epoxy, 105 Resin and 206A hardener as well as 410 microlite fairing.
>
> I mixed up some epoxy, four pumps each into a 2oz. plastic cup, added a
bit
> of fairing to thicken, and about 10 minutes into ladeling the mixture onto
> the keys, the mixture began to smoke in the cup it was in.  It had been
> slowly gaining heat the whole time.  I set it down, and the whole thing
just
> solidified within about 3-5 minutes.  I mixed a fresh batch, same result.
> Then I mixed another a bit thinner (less fairing), [and in retrospect,
only
> two pumps] and didn't seem to have any trouble this time.  What's going
on?
>
> Response from West System:
> <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
>  The more mass that is mixed, the faster the product cures.  Also, the
> longer the product is contained the faster it cures.  Ambient heat also
> accelerates the cure (for every 20F increase in temperature, pot time
> halves).  The cure mechanism/energy produces heat - exothermic.  4 pumps
> of each is a lot of material and the time it takes to blend in #410
> Microlight to a thick consistency in a container with little surface
> area, plus the ambient heat from your hand holding the pot is sufficient
> to produce a run-away exothermic condition.  Suggest mixing less - 2
> pumps each and after blending resin/hardener together spread out into a
> shallower pot when blending #410 - increased surface area extends
> working time.
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>
> Ed also pondered the idea of a cold bath/wrap to extend the working time,
> and this seems to support that idea.
>
> Hope this helps some folks.
>
> William R. Monroe
> Madison, WI
> Assoc.
>
>
>
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