WORKING WITH EPOXY
Warming vs. WarmI often see advice to warm your epoxy to improve wet-out. This is a good idea if your resin is stored someplace colder than where you are applying it to your boat. But if your boat is someplace colder like the garage, warming it up will do little except make it easier to mix. As soon as you spread a very thin layer of epoxy on the boat, the epoxy will quickly become the same temperature as the hull. In fact, I have seen a couple kayaks who's builders have heated their epoxy and then used the pour and squeegee method. The initial pool of epoxy was warm and soaked into the wood a bit more than the epoxy that was spread out from the initial pool. The result was a permanent dark blotch where the epoxy first hit the boat.
What does work is to warm up your shop well before performing your epoxy work. Then let your shop cool down somewhat afterward. This will let contracting air within the wood will pull resin into the cracks and fibers for a good seal. Be aware that epoxy cure rates are very sensitive to temperature. At 90 degrees it can be measured in minutes and at 40 degrees it can be measured in days.
Another good way to seal joints and hard to reach areas is to gently warm them with a heat gun and then apply some resin. The cool down will draw the resin right where you want it.
End Pour ThoughtsThe problems presented with end pours results from the fact that epoxy resin shrinks when it cures. If you make your end pours all in one batch, besides the risk of getting too hot, bad things can happen. Since the resin is going to shrink, something has to give. Either the hull will deform inward, the resin will crater, the resin mass will develop internal fissures, or some combination of all three. Obviously unseen fissures are not desirable, nor is wood put into permanent stress. All it takes is a nice hot summer day in the sun and glass starts showing white stress marks or strips move around.
For those filling the ends on stitch and glue designs before the deck is on, it's common for the hull ends to pinch inward, thus making for a mismatched fit with the deck.
To test for the presence of internal fissures, I poured left over resin into a stout tube. Sure enough, when I cut it open later, there were a couple of large lengthwise cracks.
Personally I prefer to install small blocks of wood instead of pouring in heavy resin. I fashion a block to fill up an area just large enough to cover the future toggle rope holes. The blocks are glued in and sealed with epoxy. To install the deck I squirt thickened resin on top of the blocks and tape the deck down making sure there is plenty of squeeze out.
If you want to pour resin, you can do it in small batches to avoid the large shrinkage problem. Or make a dam and fill it most of the way with left over batches before the deck is installed.
If you do your end pour all in one batch, at least follow it up with a small batch of thin resin to seal possible cracks.