Howard,
If you have any left over from your door sill project, you still could use it on model airplanes. Trust me, it isn't that bad.
I continue to be leery of using alcohol and a bare finger that so many guys recommend. Alcohol apparently has a property of penetrating the skin fairly easily, and introducing any kind of epoxy resins into your system can lead to medical issues. Guys that work with epoxies a lot, like homebuilt airplane guys or boat builders find that a certain percentage of the population suddenly gets sensitized, and future work must be curtailed. And you don't know until you hit that wall. All the guys who seem immune will say it is not an issue. And maybe they will never be affected. But lots of others are, and you can't "undo it."
A few years ago, I was getting ready to put fillets on the latest model, but when I opened the Epoxolite, it had hardened and was no longer usable.The tests I ran on the different materials used techniques and tools that I had evolved for Epoxolite. So I modified as seemed necessary when I saw how the different materials I tried reacted.
1. EZ-Lam epoxy (30 minute) loaded with wood flour (balsa). Still pretty heavy. Hard to sand. Difficult to smooth out. Did not readily wet out and adhere to balsa substrate. Seemed like the wood flour absorbed all of the stickiness of the epoxy. Pinkish color. (I tried this first because it seemed possible this was similar to SIG’s recipe. If so, it was not close enough to get the same good results.)
2. EZ-Lam epoxy (30-minute) heavily loaded with colloidal silica and microballoons (50/50). Stiff mixture that stays put, but cannot be smoothed out with wet wiping techniques. Pebbly finish. Very hard to sand. Medium gray.
3. Wetter mixture of (2), with less silica. Smoother, but still hard to sand. Medium gray.
4. Polyester filler (Bondo). Ran test just for comparison. Sands easily. Hard to smooth out wet but might be easy with better technique. Heavy. Uncertain compatibility with finishes. Future shrinkage issues? Pink.
5. 30-minute epoxy heavily loaded with cabosil. Cabosil makes it thixotropic. Hard to sand, Not flexible. Mediocre surface finish after wet-wipe. I lost this sample, so I do not know which kind of epoxy I used.
6. Super Fil. Easy mix. Light weight. Smoothness and spreading almost as good as Epoxolite. Not as “sticky” as Epoxolite, so a bit more work to trowel into corners, and probably not as good for making structural joints. Not hard to shape or sand. Blue.
7. Minimalist fillets. For quick jobs, I now simply stand the plane on one wingtip and put a bead of regular 30-minute epoxy in the corner. Wet out the edges and let it do the meniscus thing. It actually works pretty good. Note that any epoxy that mixes 50/50 already has filler in it, according to the bonding experts I used to work with. Clear with yellow tint.
So after trying all the stuff I had on hand in tests 1 thru 5, I ordered some Super Fil. The project sat a couple of days but not a big deal. After trying the Super Fil, it was so much better than the others that I stopped any further tests. Other methods and other combinations might produce something with results equal to Super Fil, but I was a long way from it.
I think results are highly technique dependent, and one person’s acceptable might be 10 rows back for an expert builder. And without seeing one another’s “acceptable” you can only guess whether it would meet your standards. These were my observations, for what they are worth. All my planes since these tests use methods 6 or 7, depending on what it is.
Dave