What you are experiencing is what I feared most when I found out MGS was being distributed to homebuilders. Although these are fine resin systems for which they were formulated for (factory built gliders - motor gliders, wind mill blades), they inherently exhibit this peculiarities from time to time that puzzle the un-knowing.

Because these products are primarily cycloaliphatic amines and stericly hindered polyoxyalkyl amines accelerated with copious amounts of unreactive ingredients, they tend to be sensitive to temperature during cure. If it is too cool, (below 70F in my book) they will slow down dramatically of course, but they can "B-Stage" as well. This is a physical state where the resin is neither liquid or cross-linked sufficiently enough to be called a plastic. It is "vitrified" and depending on how much is has crosslinked, it can be a sticky taffy like substance to a brittle friable solid. Once it has achieved this vitrified state, it can take a considerable amount of time for it to continue curing past that vitrified state - if ever. Sometimes, it is quite easy to mistakenly identify the brittle friable solid as genuine cured plastic state. NOT GOOD. HOWEVER, in most cases, with the addition of heat you can "re-start" the curing process and drive it to completion. THIS IS WHY MGS recommends a post cure for their resin systems.

If you must use the MGS systems, please be sure your room temperature is at least 70F. Especially if your going to use the slow curing agent.

I have talked about the importance of temperature control many times before. It is always important to control the "room temperature" at which ALL your building materials are stored at prior to their use. I think it is well worth the money to buy a window air conditioner for your garage or shop area. It reduces the overall sweat factor.