You know the scene at the end of any action movie where the hero has minutes to disarm the bomb, cutting the wires in just the right sequence or he blows up the 747 full of schoolkids? Working with epoxy is just like that.
In short, using epoxy involves mixing two dangerous chemicals together to make a viscous adhesive so powerful it permanently bonds anything it touches. You have minutes before it reaches critical temperatures and kicks off like a bomb. And if you do it wrong, at best, you completely ruin your work, and at worst it burst into a violent conflagration.
Okay, that’s overstated, but isn’t really too far from the truth.
Back in the day there were a few waterproof adhesives that were used for boat building. I’ve never used them, so for me, they are largely mythical. Some came in powder that you mixed with water. Some had multiple parts you mixed together. But for the last several decades, epoxy is king.
Until I started researching boat building methods, I really didn’t understand epoxy. Epoxy was just something I squirted out of tiny twin tubes now and then to fix something that wouldn’t stay together with a liberal coating of Elmer’s. Who would have thought I’d be brushing epoxy on to 2x4s and plywood with a paintbrush by the bucketful?
After wading through books on fiberglass boat building, I’m wise to its ways. Epoxy is simply a hard plastic that comes in (generally) two parts that you mix together and apply as a viscous liquid. The formulation contains a resin and a hardener — and several other things including stabilizers, thinners, accelerators, decelerators, fillers, and sometimes waxes — that together make a polymerized plastic goo. When hardened, it is much stronger than the wood it is adhering together. Two pieces of wood epoxied together are for all practical purposes one piece of wood.
Epoxy is commonly the stuff that is used with woven glass cloth to
make fiberglass. Together, the two make a super tough, resilient
The reaction of the resin and
hardener is exothermic and sets up hard as the result of the heat
generated by rapid oxidation. What that means, is that from the moment
you pour the hardener into your resin, the clock is ticking.
Chemicals in epoxy are varying degrees of poisonous. It is recommended that you wear eye, skin, and respiratory protection. In practice, we regularly only used skin protection in the form of a release cream for our hands and latex gloves. Principally because the epoxy is uncomfortably sticky and once stuck to your skin, more or less permanent.
Kai had some experience with epoxy (she helped her dad fiberglass his submarine!), so that helped take the edge of terrible uncertainly that was epoxy for me. Still, it is stressful. Preparation, planning, and timing are everything.
We had the “slow” epoxy formulation that under ideal conditions (70-80 degrees Ferenheit, medium humidity) takes an hour to set. What were ideal conditions for us, a sunny barnyard, were less than ideal conditions for epoxy. We had about 20 to 40 minutes to work with the epoxy before it rapidly started turning hard as a rock. Despite all of our planning, we had a few containers of epoxy kick off faster than we could use them, resulting in a few hard plastic hockey pucks.
Before any complicated assembly we carefully discussed our game plan before we committed with the epoxy hardener. A simple plan might look like this:
- Set up the epoxy station, level the surface (for volume measurements).
- Get the drill ready with the extension cord, correct star bit, and screws.
- Put wax paper under everything.
- Turn the pieces adhesive-side up, mark places to epoxy.
- Measure out single batch of resin, do a final check.
- Add hardener and stir for at least one minute, scraping the sides.
- Apply first coat to all surfaces to be adhered.
- Measure out 2nd single batch of resin, final check.
- Add hardener and stir for one minute.
- Add filler (silica) to thicken.
- Apply 2nd coat of thickened goo to one surface.
- Assemble pieces, screwing as you go.
- Smooth out excess goo that may have squished out
As recommended on the Glen-L Waterlodge plans, we used epoxy to
adhere every single joint and piece of plywood together. We used it to
“encapsulate” piece of wood, that is, seal them completely in epoxy so
they are waterproof and rot-proof. And later we will use it to cover the hull of the boat in fiberglass.
So when you see in future build days that we say something like “assembled side stringer,” understand that this means cutting all the pieces, assembling them for fit, and epoxying and screwing every single joint.