Just found your site today, but been doing composite work professionally and for fun for 20 years, everything from Cigarette boats, to world record Hydrostream blueprinting, and if i may add my 2 cents on the subject;
If a surface is cleaned well, with a clean rag, and scuffed with with 36 grit, and scratched with a wire brush, even the cheap old Bondo brand polyester and talc filler patches most anything. if you don’t want it to “pop” at any point, once hardened, paint it, or better yet, scuff it with 80 grit, and brush a layer of epoxy over it, to seal the talc. Overall, we like to think cheap stuff does not work, which is why people buy expensive cleaners when borax and vinegar will clean most anything. I can’t tell you how many times i have used Bondo has a quick and simple fix on something, and had it last 10 years without a problem, rarely do I have it break loose if prepped and sealed well. A frined of mine was an engineer for an outboard manufacturer, and told me they used to use bondo as an adhesive even on parts that were exhaust “stuffers” right next to the exhaust ports. He swore the stuff would not smell and kept adhering after multiple cycles. Obviously, not recommended. Another friend is a world record holder in 13 foot racing power boats, with 70 horsepower evinrudes, doing 70 mph (on a v-bottom boat), and he also happens to be a physics professor, and he, also, blueprints his hulls with bondo. Is is technically inferior, yes, but is it strong enough? absolutely, for most applications within reason.
