Shelf life for resins

[Ross]

I keep reading that epoxy and ester resin has a finite shelf life but my experience has been that they are viable long past the use by date. I have a gallon can of Evercoat polyester resin with a screw top that I have been using from for at least five years and used some last night for a minor repair and it behaved entirely predictably. I have an Evercoat brand epoxy kit, quart size that I bought several years ago when the store was closing it out . I have used small small amounts and see no change from one year to the next.
So I am wondering if others have found this apparent shelf life to be the case. Does the resin lose some of its specified qualities with time but still react in a normal fashion? I am not making major structrual repairs so ultimate strength is not a concern for me.

 

[Alan]

Ross,

I have found the same thing. I've been using West System in a gallon can that a friend gave me after doing major renovations to his boat. It's approching 10 years old and still seems to work fine.

 

[RichH]

Yes they do have a 'shelf life' ... and that shelf life is usually determined by testing in 'slightly worse' conditions than would normally found where they are stored. So the consumer gets some 'safety factor' inbuit to the shelf life. Chemical reaction is mostly denpendent on temperature. The typical is most reaction rates DOUBLE for every 20 deg. C (68°of F) of temperature increase. So applying the same rules to your stored resins at a temperature cooler than what was used to create the spec (probably 100°F) you can easily 'approximate' by calculation the 'change' in the 'shelf life'.

Storing in cold/cool environments will usually always extend the shelf life --- look what it does for food where spoilage is mostly a bio-chemical reaction.

Such a calculation is a simple arithmetic ratio of temps and known 'rates'.

 

[Ross]

I had some resin that I bought in five gallon containers and as long as they were tightly closed they kept fine but if I left the screw cap loose they would start to harden without any added catyllist. I was told by my supplier to just strain out the lumps and use it. My resins are kept in the garage and the temperature can range from 25 f in the winter to well over 90 f in the summer.

 

[kenn]

I have what's left of a gallon of EAST System epoxy that i bought about 3 years ago. It's been mostly in my basement, though I do confess that it spent about 3 weeks in my truck while I was doing repairs, so I've probably aged the stuff very rapidly. But it still seems to set properly.

Slightly off-topic - I finally got to see what happens when alot of epoxy 'kicks' in the container. Hot, sunny day, I mixed up about 4 fl oz (...alot) in a clear plastic cup, then it sat in the sun while I futzed with some glass cloth. I started to use the epoxy and noticed that the cup was warm. A minute later I noticed that the cup was VERY warm. I quickly tossed it to the ground. It got hot enough to melt the cup and this deformed "epoxy monster" reached out of the cup, then the whole mess hardened. Took about 3 min total.

Lesson- don't mix up alot of epoxy then leave it in the sun.

 

[Hermit Scott]

I bought a quart size of bondo, the regular car stuff to make a mold for vacuum forming some plastics. I never used it and it sat in the Texas heat for 2 years in my shop. I was going to skim coat the inside of my boat where I filled in all the ports and there were science experiment grade crystals formed inside the can. They looked like rock candy.

I had some resin that I left in a dock box and it appeared to get darker in color the longer it sat. I used it and it worked just fine.
I finally finished one side of the ports outside. Now I have to sand it flat. That side was in the shade. I tried to do the other side in direct sunlight, and I had about 60 seconds before the resin kicked. I guess when I go to finish that side I will have to turn the boat around out of the sun.

 

[packman]

word of caution!

Most of you already know this but shelf life dates are there for a reason. Manufacturer testing is done with an eye toward safety and the dates are before the point where the materials FAIL some or all of their design criteria. I have seen materials recertified after they're considered "shelf worn" but this is done after careful testing in a lab equipped for the purpose. Just my opinion, but I would not use out of date material for anything I might have to bet my life on.

 

[Ross]

Re: word of caution!

I got this reply from U.S. Composites:
Ross,

If they are still curing, you will experience no loss of anything – strength, quality, etc. The only thing is they may change color – become more yellow but if they cure, they will work just as good as new.

Thank you,

Nan

 

[RichH]

Ross, you got 'weasel words' in this reply : "become more yellow but ***IF*** they cure, they will work just as good as new". also meaning if they DONT cure, then they wont work as good as new.

 

[Ross]

My email to US Composites stated that the resin poured, mixed and cured in an apparently normal manner. So my concern was a loss of the unseen properties.
I have observed that the catylist MEKP will degrade and not effect a cure. I always mix a test sample of 2-3 ounces and allow it to sit for the expected times for the gell and glass stages.