I first considered adding lite ply or balsa to the CF but I didn't like the idea of all the sanding and especially didn't like the idea of a soft surface that had to get additional multiple layers of laminating. Second thought was to use a bunch of filler, like SuperFil, and again sand to shape. The worry I had with this method, besides again, all the sanding, was that I could see the filler chipping/chunking off over time. It was then I remembered I had faced a similar problem of getting a secure base of large, thin fill areas when I did
the re-finishing of an antique dresser for my wife. Better, yet, I still had some of the
US Composites Kleer Koat sitting on a shelf down in the basement.
Before starting on the fins themselves I wanted to do some testing of the epoxy to see if it would fit the application. Two issue with use on the fins are: 1) would the epoxy layer adhere, especially in the areas where it transitions to an ultra-thin edge and, 2) would it be stiff and shatter or would it be flexible. I felt somewhat comfortable with #1 above after my use on the antique dresser, but less confident in #2 as the prime application for this epoxy is bar and table countertops which are clearly fixed surfaces with little/no flex.
So to test, I took some scrap pieces of plastic packaging from a tool I had bought and cut it up into pieces so I could simulate ~1/8" thick fill that transitioned into thin leading/trailing edges. I tried two pours, first the epoxy only with no filler as it is meant to be used (i.e., clear table top application). I also did a second pour with phenolic sphere fill as this filler typically will provide the finished epoxy with more flex. I left the epoxy overnight and took a look this morning. What I found was:
1) The epoxy cured solid with no filming and/or soft spots. In the picture below you see the two main samples, with and without fill. Note the one without fill did have a bit of overspill as can be seen.
2) The epoxy cured into a nice sharp thin edge on both samples.
3) I was expecting to be able to pop the epoxy out of the plastic mold as most epoxies don't adhere to plastics. This epoxy is not one of them. I had some extra of the filled sample and put it in a deeper mold--in this case I cannot even cut/rip the mold off around the epoxy. So the adherence is great--good news for my fin application.
4) Finally the last issue I was worried about was flex. Again, presently surprised. Both samples flexed well, with the filled sample performing better, i.e., easier to flex across a greater distance. In the extreme case, I am able almost to make a "C" shape with the thin edge of the sample (medium bend shown below).
So, after this morning, I am happy with the application testing of this epoxy. Also nice to be able to use the US Composites Kleer Koat as I had nearly a gallon left over from my first project. Never thought I would find an application for it! In the next few days I will begin working on the spine pieces and begin filling the Honest John fins so "more to come."