I've had my first experiences with a PU resin (Xencast P6). I get decent castings but after demolding the casting is sweating an oily substance. Is this always the case with PU resins? I switched from epoxy to PU to increase production, but now I have to leave them sweating a few days and clean the parts.

I am casting a 15mm thick part in a 2-part mould CNC'ed out of Renshape 5173 pu toolingboard. The release agent is Easy Lease. I shake Part A thoroughly before mixing.

Hi,

There can be several reasons for the cured resin sweating.  Slight inaccuracy of either part A or part B when measured can lead the excess component being sweated out.  Improper remixing of the settled sediment can cause it too.  Other issues can be the resin isn't quite fully cured which is usually a temperature issue so a quick post cure will solve that.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thank you for the reply. I mix Part A + B very carefully (35+35 gr, accuracy: 0,1gr), pour it immediately and leave it. I found this on the smooth-on website:

https://www.smooth-on.com/support/faq/157/

Maybe it's just a bit too cold. For the next batch I'll try heating Part A + B to 23C before using it.

cold temperatures won't help for sure. Cold temperatures can cause all sorts of issues with resins as well as the more obvious increased cure times.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant