I am actively overhauling (not restoring) a pretty rough but not really damaged Kevlar MR Malecite canoe and have a couple questions. First what is that strange elongated diamond of off-white color in the bottom inside of the hull? It simply looks like some paint or possibly a weather/skid resistant coating. Not sure because mine is pretty worn off in some places. Second,… this canoe had some significant impacts and major spider-webbing (cracking) of the outer gelcoat and two areas are quite soft with slight areas of Kevlar material damage barely visible,… SOOO I am going to lay a couple of layers of S-Glass and G-flex on the inside to stiffen it up without adding to much weight. My question would be, what do I need to do to the existing Kevlar surface in order to prepare it for proper adhesion of the new layers? These patches are almost exactly opposite each other where the stern paddler would kneel so I am going to make identical size oval patches about 18" by 8". I am going to make it look as symmetric as possible. It was forest green with what looks like aftermarket mohogany gunwales but its going to be turquoise when its done.
MRC often painted the bottom of their Kevlar canoes with a flat gray paint for UV protection. It did tend to get scratched off.
To patch the interior, I would just sand and clean the areas well. If you use something like 100 grit paper and don’t get too aggressive, you will just be sanding the resin and not the aramid itself. Clean well with acetone after sanding.
I would not use G Flex for the patches. It will work but it has no special merit for the repair of a composite canoe and a couple of distinct disadvantages. It is a little more laborious to wet out cloth with G Flex, although that is not a major deal. But G Flex is significantly more expensive than conventional epoxy. Most importantly, it does not cure clear like conventional epoxy does and the repairs will be much more noticeable. One layer of 6 oz S-glass fully wet out with conventional epoxy with the weave of the fabric completely filled will be nearly transparent. A multi-layer patch will be a bit more noticeable, but much less so than if you use G Flex.
Thanks a bunch! I was about to go buy $80 of Gflex. I have conventional fiberglass epoxy that should work. Really appreciate your response. I suppose Gflex is best for exterior abrasion areas like stems and skid plates and small repairs. Right?
G Flex was a special formulation of epoxy designed for better adhesion to plastics. It is definitely the epoxy to use on ABS or polyethylene, although getting a good bond with polyethylene does require pre-oxidizing the rather chemically inert polyolefin surface chemically or via flame oxidation (usually the latter). G Flex also has a lower Young’s modulus meaning it retains greater elasticity when cured. This lessens the compliance mismatch that tends to occur when conventional epoxies are used for repairs on more flexible Royalex boats that sometimes results in failure of the repair well after the fact. I also like the fact that G Flex can be mixed up in very small batches 1:1 in volume by eye, which makes if very convenient to do small repairs without wasting epoxy and means there is no need for mixing pumps.
But G Flex is significantly more viscous than conventional epoxies which means it takes a bit longer to work it into cloth to fully wet it out Composite boats are already pretty stiff so there is no need for a more flexible epoxy…