Filling the Voids

I spoke too soon in my previous post when I said that I was finished with grinding and other demolition. A closer examination revealed the need for a bit more deconstruction before I'd be able to start patching things back up. This post covers three sessions of work.

I cut back still more loose, thin material from the stern. Even though there was still material that should have come out, eventually I had to stop in order to maintain the basic shape of the hull. Still, that big gap is a couple of inches long and an inch wide where it goes all the way through, and its full length in the outer surface is about eight inches.

I used a saber saw to open up a couple of cracks in the bottom, amidships, that extended all the way through the hull. Being slightly wider, the crack will now be easier to fill properly with epoxy. I used a chisel to bevel the edges of the crack to increase the surface area for bonding.

Back at the bow again. The hull was warped so that the two sides of the gap didn't line up. I screwed a cleat across the gap to bring them into alignment, placing some plastic packing tape on the underside of the cleat so that epoxy won't stick to it. Then I covered the gap with two layers of waxed paper and taped it into place. I did the same with the cracks amidships.

Here are the materials I'm working with at this stage: West System G-Flex epoxy (in bottles), and G-Flex filled epoxy (tubes), plus colloidal silica as a filler. I've used regular West System epoxy before, but this was my first experience with G-Flex. Even the "liquid" version is very thick and difficult to stir. The filled version is nearly the consistency of a paste.

More materials and tools: latex gloves, paper cups and bowls, mixing sticks, acetone (for cleanup of tools and drips: not for skin). Turns out the G-Flex is too thick to use with the syringes (package at center). Not shown but also important: acid brushes, plastic spreaders, waterless hand cleaner.

I started working with the liquid epoxy, filling the smaller cracks and coating the surfaces of the larger ones. In order to improve flow, I warmed the epoxy in the mixing cup with a heat gun before brushing it on with an acid brush. First I coated the outside of the stern, making sure that the striations from the plastic welding were well-coated. Then I turned the hull over and did the midships cracks from the interior (shown).

I mixed a batch of the filled epoxy but quickly realized that even that was a little too runny for the large gap in the stern, so I added a heaping tablespoon of colloidal silica. It was hard to mix the light, fluffy filler into the stiff paste, but after a lot of stirring, I was able to achieve the consistency of peanut butter. This served nicely when applied with a plastic spreader, and the waxed paper on the outside sufficed to keep it from falling through. Notice the screw heads holding the cleat on the outside of the hull: I tried to avoid getting epoxy on them, to make them easier to remove.

G-Flex has a long cure time even at 70 degrees, and the basement where I'm working is considerably cooler than that, so I set up a tent over the canoe using tarps and insulation board, and placed an oil-filled electric heater (no fire hazard) inside it to hasten the cure.

Three hours later I untented the boat, flipped it over, removed the waxed-paper patches, and filled the gaps and depressions on the outside with filled epoxy, applying it in two layers with a tent-cure in between. This is the midship patch after the second application, now ready for a light sanding and covering with kevlar.

The filled epoxy on the inside was enough to hold the edges of the stern gap in alignment, so I was able to remove the cleat before applying filled epoxy. This photo shows two epoxy applications in place after curing. Although I tried to apply the paste as smoothly and evenly as possible, the hardened surface is (inevitably) somewhat rough. This will all be covered by a fresh layer of kevlar, and then much of it by a skid plate. I won't decide how much of the patch to sand and grind until I've received the skid plate kit.