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

Thanks for immediate response . How would you recommend what point of humidity is advised not to pass to expect good hardening process ? 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I'm asking particularly about XCR resin. Anyway gonna hang higrometer in workshop. Probably I will report you more precise numbers .

Unfortunately there are too many factors and variables at play which can have an effect on how sensitive to moisture the resin ends up being in a set situation.  Hence no precise manufacturer data tends to exist.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Hi Warren.
I'm worried about XCR resin behavior. I have put one layer of hotcoat on EL2 resin. It feels a little sticky even after 4 days of curing. This time temperature and moisture in workshop was controlled precisely between 21-22deg.C and 40-45% moisture. Anyway it's not possible to sand it dry. It clogs even 60 grit sandpaper immediately. See attached batch numbers of that XCR epoxy. Because XCR resin that I bought last year had much better properties. It dry sanded easily.
Here you'll find a link of short movie that explains it  :  https://we.tl/t-OYbCn5oCzj

I've ordered 1kg XCR yesterday. Will see how it behave. I have suspicion that only this particular batch could have problems. If that will prove, I would like to return one unopened 5ltr package. 

Strange that you have more issues. that batch last sold about 3 months ago so is less than 5 months old overall.  We haven't had any reports of issues yet so it is useful to work out what is going on.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

The resin underneath is hard. It looks like it is covered by thin softer ( waxy ) layer.