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.)