Hi John

: I'm not sure I understand, did the container itself shrink, or did the
: contents shrink?
: Here in Australia West Systems hardener (no MAS) come in bottles half full.
: Is that the case with MAS also? If so how did you determine that there is
: evaporation?

No it is a full 1/2 gallon plastic container, just no seal other than the cap. The container was visibly caved in a bit, enough for me to be sure I would have noticed it if it had been like this in the store. It also happened with System III containers that I thought I had sealed well. Not with a Fiberglass Hawaii home brand that came in an metal container. Just wondering if something can get through the plastic and if so, what.

Henk