My first "Hold-Heet" glue pot, which I purchased circa 1964, has a
copper inner pot. It has never corroded.

In the 1980s, I bought a second "Hold-Heet" pot so two of us in thew
shop could use hot glue at the same time. (We often keep thicker glue
for pumps in one, and thinner glue for pouches in the other). This one
had an aluminum inner pot. After about ten years of daily use, the
bottom corroded all the way through. The corrosion occurred only where
the inner pot was in contact with rivets located in the bottom of the
outer housing. (We never use the pot as a double boiler. That is, we
always mix the glue directly in the aluminum pot, not in a glass bottle
sitting in water in the pot. The corrosion occurred only in the bottom,
not the sides.)

When I ordered a new aluminum inner pot from the manufacturer, I asked
if the company still made copper pots. In a friendly way, the salesman
implied: "Are you living in the dark ages? Copper is expensive these
days!"

Before using the new inner pot, I cut out several little pieces from a
strip of scrap aluminum approximately 1/32" thick, and epoxied them
under the rim. They are just thick enough to hold the inner pot up so
the bottom doesn't touch the rivets in the outer housing. There doesn't
seem to be significant loss of heat transferred into the pot. However,
with no contact between the rivets and the inner pot, there has been
no further corrosion.

By the way, we always keep each glue pot covered except when we're
actually using the glue brush. One cover is made from a plastic lid
from a coffee can, with a hole punched in the middle for the brush
handle. The other cover is a heavy rubber disc from one of those
sanding/buffing discs that fits in an electric drill. It already had
a hole in the middle where the mandrel was attached. The cover keeps
the glue from drying out too fast.

When we're gluing gaskets that have little reason to separate from the
wood, we keep using the same glue day after day. When we need strong
glue for gluing wood to wood (e.g. pneumatics to deck boards) or for
covering pressure pumps, we make a new fresh batch.

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