I'm using XCR coating resin since last year. And never had difficulties to sand it dry. If it was hardened for at least two days, dry sanding always went smooth. But I've experienced the opposite this Summer. When it was impossible to dry sand resin that was hardened for 4-5 days. It clogs sandpaper or Abranet immediately. Also noticed weaker adhesion properties of that resin, no matter that previous coat was sanded with 220 paper. I have suspicion that it has a lot to do with air humidity. But maybe there are some additives available that would help to avoid such problems ?

The formulation of the resin has not changed so I would not expect the behaviour of the resin to fundamentally change.  It could be environmental as you suspect, although you would expect it to settle as the weather cools.  There are not any additives to add to it to change the properties in that way unfortunately. There may be some humidity in the air where you are causing a few issues.  Here we have had humidity well above 80% RH for a while.  Humidty alone could be responsible as the moisture might compromise the cure which would result in poorer adhesion and a slightly softer resin causing the sanding issues.   The heat would also mean the resin is likely to go past the B stage much quicker and thus naturally harder to get a bond between layers.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant