On 10/13/2010 1:12 AM, David Nebenzahl wrote:
[Well, not new, just new to me]

Now we've all used epoxy sometime in our lives. at least to glue
something back together. I've done that many times, but I never used
liquid epoxy until today, when I came to the part of my door-restoration
project where I sealed the outside of the door with marine epoxy. My
experiences with this substance follow. Long post, be warned.

Just for background, the project is re-facing a beautiful Craftsman door
whose plywood skin had started to delaminate badly. The door is a big
(42") door with nine beveled lites of various sizes, and was at one time
very nicely covered in oak-veneer plywood. The original plan was to try
to restore the veneer on the face. After doing a partial repair a couple
years ago where I reglued just the top layer of veneer, I determined
that this was beyond my capabilities and started asking around at local
shops. To make a long story short, the answers I got were either "can't
do it" (would have to replace all the glass with safety glass to bring
it up to code, etc.), or the job was prohibitively expen$ive.

So we decided I'd just reface the door, restore the top surface and make
it smooth and level, and paint it. Keep the old Craftsman design, just
lose the natural wood facing. So I peeled off about half of the old
plywood (mainly from the bottom half of the door), cleaned up the
surface, and glued on new 1/4" marine plywood (HydroTech). Also pieced
in some of the old oak veneer I had left over in places where only the
top layer had let go, leaving a solid substrate. This left lots of
discontinuities and gaps, since the plywood I used wasn't exactly the
same thickness (and in some cases had been glued over the bottom layer
of old veneer which was still well bonded). So I filled these in by
gooping on lots of PC-Woody (basically a wood-epoxy paste).

Today I arrived to smooth down the surface and seal it. Sanded it
smooth, mixed up the epoxy and went to town. First time I'd ever used
this stuff; I ended up getting West System 105, and their slow-setting
206 hardener, on the suggestion of the people at the local West Marine.
(Turns out West System is from a different company.)

It went on easily, and was much less nerve-wracking than I'd expected.
(I always get anxious around *anything* that sets, hardens, catalyzes,
gels, or otherwise changes state. A tube of caulk can cause heart
arrhythmia.) It basically went on like fairly thick varnish. Soaked into
the wood surfaces nicely.

I chose the slow hardener because I knew it would be hot this week.
Today it was close to 90° in Berkeley where I was working. I thought it
would be better to risk a long set time (the back of the can says 10-15
hours for "cure to solid") than to risk having the stuff harden up while
I was still trying to brush it on. Turns out I made the right choice.

I mixed up what I thought would be enough plus a little more (another
anxiety-producing dilemma: too much or not enough?). Better to err on
the side of wasting some rather than running out before covering the
surface, thinks I. About half-filled the plastic mixing cup I bought. I
got it all on in about 10-12 minutes, with the epoxy still liquid, when
I noticed that the bottom of the cup was getting warm. *Very* warm.

Now they warn you that the stuff is exothermic: "Curing epoxy generates
heat. When contained, a large mass of curing epoxy has a very short
life, and can generate enough heat to melt plastic and foam, burn your
skin and ignite combustible materials".

It's just very strange that this reaction happened well after I mixed
the batch, and after I'd used most of it. The cup got very hot, and I
noticed the material was actually smoking a little, and gelling up. It
all happened very quickly. Fortunately, I was just about done; I just
mixed up a smaller batch in another cup and finished up. By the time I
was finished brushing on the second batch, there as a big solid lump in
the first cup.

So apparently this stuff behaves differently from most other setting
materials: the more stuff there is (large mixed batch or thick coat),
the faster it sets up. In my case, it was just about perfect. I was
worried that I'd have to hang out at my friend's house way past sunset
with a sticky front door; it set hard to the touch in just a couple hours.

The West System stuff is pretty cool, if expensive; I bought the pumps
they sell which are made to go into their cans. Just pump the same
number of strokes of resin and hardener, and you get a perfect mix. No
measuring. (I'm guessing that other brands must use this system too.)


Epoxies can comprise a wide variety of materials running from liquids
like you describe which can be cured rapidly (or slowly) to solids
requiring long, high temperature cure.