[phapp]

Discovered that even with clean, well sealed caps, opened polyester resin has a shelf life. I noticed that the color was very dark and it did not set-up at all after 24+ hours (yes, proper amount of hardener and thoroughly mixed, and warm enough). Also the hardener did not have that acrid smell.

I'm guessing mine was between 3 and 6 years old.

Fortunately it was only the first pass at modifying my rudder bottom fairing and cleanup for recovery / redo was not bad.

Trying to be smart, I tested a newer (<3 yrs?) can (also opened) and it has not even begun to set up after 3 hours.

Now I'm testing my newest can with brand new / unopened hardener. The resin color was much more like I remember it (light amber) and the hardener had that acrid smell as soon I punctured the seal. All were Evercoat from Aircraft Spruce. We'll see if my newest batch is any good.

A google search confirmed that both have pretty limited shelf lives:
http://www.practicalmachinist.com/vb/general/ot-getting-old-fiberglass-resin-harden-157575/


So if fiberglassing is coming up on your build schedule, you might want to test and or be sure to have fresh stuff on hand lest you be delayed by needing to buy more. I'm pretty sure you can find the polyester just about any place local. Auto parts, hardware stores, Home Depot, etc. I will do that if I need more.



-8 QB

 

[Bob Kuykendall]

Discovered that even with clean, well sealed caps, opened polyester resin has a shelf life...

This is one of the reasons I don't do much with polyester any more. Sure, it's cheaper than epoxy, but you can pretty much count on it going bad after about six months even if you never open the can. When I have a need for polyester gelcoats or topcoats, I try to only buy as much as I need for the job at hand.

On the other hand, I have jugs of epoxy at my shop that are ten years old and they still cure fine and seem to yield good properties. The resin sometimes crystallizes, but I just heat it to about 100 F and it goes clear again.