I started a new test last night to determine if I can add some extra abrasion resistance to the outside of a hull. Most of the rivers I paddle are shallow and sandy or shallow and rocky, and it's tough to bear the scratches from every single trip in my boats. Running aground is guaranteed several times every trip. I already use s-glass on the outer layer of my hulls but it still shows scratches in the epoxy even if it doesn't cut into the glass. On the boat I'm building now I laminated several strands of polyester rope onto the hull to act as rub strips, but I want something that can take abuse and not effect the hydrodynamics. So, I just received three jars of powder to mix into the epoxy fill coats to hopefully improve the abrasion resistance. The compounds I have are aluminum oxide and silicon carbide. These are sold as abrasive grit typically used for sandblasting. I have the aluminum oxide in 600 and 1200 grit and the silicon carbide in 1200 grit. They have the texture of talc powder. Both of the materials are extremely hard. 9-9.5 on the mohs scale. For reference diamond is 10. Last night I mixed epoxy and mixed differing amounts of each powder in to get a feel for the consistency. I mixed 5, 10, and 20% powder to epoxy by volume. I actually did it by weight, but the volumetric amount makes much rounder numbers. After mixing and observing viscosity I poured the epoxy concoctions into Petri plates, so I will have pucks to do scratch tests on. Observations so far, the epoxy is definitely thickened by adding the powder, but not like adding cabosil. I think I will use system three clear coat if I actually put this on a canoe, so the thickening will be negated by the already low viscosity epoxy. Even with standard epoxy at 20% powder the mix is still nicely flowable, but certainly not like straight epoxy. I thought the aluminum oxide would be the one I would actually use on a boat because it is white. It is actually more dense than the silicon carbide but not as hard. When it's mixed in the epoxy becomes a light grey. It is still a pleasing color but not the pure white I was hoping for. The silicon carbide I got is light green, most offerings are black. When mixed in the epoxy it becomes a pale olive drab which actually looks much better than I expected. Once the pucks are all set up I'll go about scratching them with various implements; screw drivers, rocks, sand, etc, so we'll see if it's actually worth adding. After my base scratch tests I'll actually lay up some fiberglass tape and use the abrasive powders in the fill coat. I think I'll have to put on a final fill coat of straight epoxy, because once this stuff hardens it should be nearly impossible to sand, the material is harder than sandpaper. Without the final coat of straight epoxy I'm afraid I'd never be able to fair the boat. I'll report back after my scratch tests on the pucks and when I do the same to the glass laminates. This will all be an ecomic balancing act since the powders are denser than epoxy and add extra weight to the layup. I have to find the balance between abrasion resistance and weight. It might turn out that an extra layer of s-glass works out better.
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