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. 

Grinding is Finished

I completed the demolition phase of the rebuild today, grinding away all the poorly-adhered kevlar and epoxy on the bottom/outside of the hull. 

The two previous grinding sessions were done in the basement, and it created a lot of nasty fluffy kevlar/epoxy dust that could be smelled elsewhere in the house. Today was lovely out, so I brought the sawhorses and boat outdoors and did the grinding there. Much better. Brought the boat back inside for the photos.

Most of the patch is well-adhered to the bottom and remains in place, but a big section had to come off, exposing cracks, caulk and a section of welding.

Close-up of the section that was ground down to "bare" or solid material. Utility knife is for scale.

I also noticed some hairline cracks in the welded sections along the bilges (right by the point of the blade). These cracks will be opened up a bit with a knife and then filled with epoxy.

I ordered a yard of kevlar cloth and small kits (around 8 oz. each) of two different versions of West System G-Flex epoxy (one filled, one liquid). Having finished exposing all the flaws, I think I'll need more epoxy.

Exposing the Stern Damage

In my second work session on the Probe 12 canoe, I removed the knee pads and the stern deck and ground a lot of the Kevlar/epoxy patching from the sterns interior and exterior.

After doing a bit more grinding and examining the extensive cracks in the hull bottom between the knee pads, and noticing its thinness, I determined that I'd have to place a fairly large sheet of kevlar over the area to beef it up. In order to make room for that, I removed the knee pads, using a heat gun and putty knife. They came up without much trouble, then I ground the surface fairly clean and smooth.

Next, I removed the stern deck. This was attached with three stainless bolts and nuts (front/center, and both ends) and a bunch of aluminum pop rivets, which I drilled out. This gave me access to the inside stern. I used a small angle grinder to remove virtually all the kevlar, which was laid into the hull poorly, with many bubbles and gaps. It may have provided structural strength in the stern, but it was doing nothing to keep the water out. It came out easily, but it exposed some large cracks in the Royalex. 

Another view of the stern, after the kevlar was removed.

Then I went to work grinding down the kevlar on the outside of the stern. This was more problematic. Large areas were poorly-adhered, while others were epoxied solidly to the Royalex. I ground out everything that was at all loose. This exposed the black-and-yellow striated area where plastic welding had been done at some time in the past. 

The other (port) side of the stern after grinding. The striations had not been filled with filled epoxy, so the kevlar just sat on top of the striations and was not well-adhered. Everything that was loose was ground off, while some of the surrounding kevlar, although lumpy, was well-adhered. Removing it in order to create a smoother surface would probably create more damage than it would remove, so I smoothed out some of the bigger bumps but did not attempted to remove it. I also ground off most of the bigger epoxy drips.

Close-up of the stern, with a light shining from underneath, shows the extensive cracking and the extreme thinness of the remaining Royalex. This will be the most difficult part of the repair, requiring a lot of filling and fairing to make watertight, strong and smooth.

Diagnosing the Damage

I like things to be inexpensive. I have no desire to show off my means by wearing expensive clothes, driving an expensive car, or using expensive outdoor gear. I favor function over fashion.

As with clothes, cars and gear, so too with boats. I like 'em cheap, and as long as they work, I don't much care what they look like. Since I started paddling solo whitewater open canoe ("OC-1") about two years ago, I've been using a borrowed boat and keeping my eyes open for a really cheap used one.

Looks pretty fair right-side up.

Well, I just found it: an old Mohawk Probe 12: a good boat for a novice whitewater paddler like myself. But it needs a bit of work. Its previous owner is a very accomplished paddler who put this boat through the wringer over many years and many trips, making a number of repairs along the way: some of them well-done, some of them re-done, and some of them strictly expedient. He sold the Probe to me explaining that it now leaks, but the exact location of the leak (or leaks) is unknown. Some of those repairs are going to have to come out and be redone.

So this blog will be a record of bringing a nearly dead Mohawk Probe 12 canoe back to life. This is Day 1.

The bow is in fair shape.

Nicely outfitted too. The pedestal saddle and harness are worth almost what I paid for the boat.

Amidships on the bottom there's big patch of kevlar fabric partially covered with black Gorilla Tape. Both bilges were subjected to plastic welding, leaving the long patches with a striated, stripey-black surface. These appear to be sound and I'm not going to mess with them.

Close-up of the bottom midships patch.

The stern has a big, ugly patch of kevlar and epoxy. Not a bash plate: just a layer or two of fabric. And it's not well-fastened: it's popped and peeling away from the Royalex in places.

Oh oh. The interior at the stern has a sheet of plastic duct-taped in place. Wonder what's under it?

So that's what's under the plastic diaper. A single layer of kevlar, very poorly adhered with epoxy.

Gorilla Tape sticks incredibly hard. It took a heat gun and a putty knife to get it off the bottom patch.

The kevlar patch on the bottom is is bad shape too. Puckered and popped in places. You can see an edge lifting here.

Got the Gorilla Tape off the interior just in front of the pedestal, again with the help of a heat gun and putty knife. There's some funky sealer here covering some cracks or holes. It's "gives" just a little, but it's a lot harder than caulk and it doesn't soften with heat.

Closer look at the white goop just in front of the pedestal. You can see cracks in the Royalex.

Extensive use of heat gun and putty knife sufficed to remove the pedestal and the center patch of the harness that was glued to the hull between the knee pads. Both were stuck down with contact cement, which (thankfully) softens with heat. I then took a small angle grinder to the hardened white goop, and removed the remains of the pedestal rubber. The inside is now pretty clean amidships, although there are visible cracks in the area between the knees. 

The bottom midships patch after grinding with an angle grinder. I ground the edges down until I reached a place where the kevlar was solidly adhered to the ABS. But there's a hole in the middle that exposes the crack through the hull. Not sure if I'll continue grinding away until I reach solid adhesion all the way around (risky), or just fill the hole with a good solid filler and then cover up the hole and the entire previous kevlar patch with another layer of kevlar. 

A closer look at the hole in the bottom patch, exposing some of the weird white filler that was visible on the inside. The black area was plastic-welded a long time ago, evidently before the kevlar and white goop were applied..