I have two containers of PR -1 gal of Silmar 41 PR and 1 Qt of Castin' Craft PR. New containers - never opened - I opened them today and they are as hard as a rock or harder! What causes that?
Keith,
Polyester resin, Silmar 41 and Castin' Craft and others are pre-promoted which means when manufacutured they are treated with cobalt naphthenate which is a curing accelerator cnd cross linker catalyst for polyester resins. When the MEKP is added the curing is kicked into high gear. Polyester resin has a nominal shelf life of 4 to 6 months from the date of manufacture, not from the date of the comsumer purchase.
This is the reason I purchase from vendors who I know move a lot of product and I am confident it has not sat on the local big box craft store shelf for several months. Freshness is essential. Storing in warm temps is also not a good idea.
Saying all of that I have had Silmar 41 last for several months with no problem and I have had it to start curing after just two or three months. Curing in the can, fortunately for me, has not happened often.
Do a good turn daily!
Don