Did an epoxy hot coat today and got these weird sag lines when cured.
I wiped the board with a tack cloth beforehand (nothing else), mixed as usual, applied with brush (did not over worked it), walked away.
Browsing through archives, I found one where, by the description, it could be similar to my case but there were no pictures so hard to tell…it all points to resin not hot enough and too thick…would you guys agree? (my pix attached).
I didn’t think it was thick but…
also, how hot would the epoxy resin need to be (as compared to doing a lam)? i.e. how much more hardener?
Always mix epoxy exactly to the right amounts. Eeither by weight (which I prefer) or by volume, both are usually not the same proportions due to the different density of resin and hardener. Getting the proportions wrong just means parts of the mix won´t harden and it will stay cheesy and will be weak. Always be precise with the proportions and always stirr thoroughly.
Anyhow…Your pictures look exactly like a problem I had maybe 2 years ago. Absolutely the same.
I made a couple of boards with that type of epoxy and everything was fine. Suddenly after a couple of boards those “cracks” appeared. When I walked away, everything was fine. 1h hour after applying the coat, those “cracks” apperaed… As if the resin shrunk while getting hard. Even the thin layers of the leftover resin in the mixing buckets showed those cracks on the surface. I made several tests, ruling out himidity, contamination and all other possible mistakes. Only mixing some resin in a clean cup with a clean stirring stick. Poured it in different buckets and such. And every test piece had the same problem.
I never found the reason for the problem. Changed to another epoxy brand and it never happened again.
Have heard of Kenetix, but never seen any over here in the U.S. With that as a qualifier; I have always mixed Epoxy as per Manufacturers Specs. 2:1 3:1 etc. I don’t think it is recommended to add more hardener. I know people do this, but not usually recommended. Various resins usually have a slow and a fast harder available. The use of Slow is fine for a laminate, but I would prefer “fast” for a hotcoat. Hotcoats are meant to set fast. The longer it takes to set, the more likely there will be problems. Sags,runs and separation.