Does epoxy have a shelf life?

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Established Member
24 Aug 2008
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Essex/ Suffolk border
I did some fibreglassing 8 or 10 years ago, and have some of the resin left. I have need of some epoxy for a repair, but it must be 100% reliable. Will I be OK using the old stuff, or do I have to take out a mortgage and buy some new?
If sealed I have not found any problems but once opened it does start to deteriorate, it gets thicker and harder to mix. Bond still seems good though on the products I have used. Do a test piece or contact the manufacturer for details.
Yes it does. once opened it's normally a year or so, harder is less. if it's needing to be perfect, don't risk it.
MikeG.":1bu6ln7s said:
I did some fibreglassing 8 or 10 years ago, and have some of the resin left.

Presume you have the hardener too... and depending on make/manufacturer it'll be probably be (roughly) a 4:1 ratio.

The hardener (mainly) is very hygroscopic and will readily absorb moisture. You can tell this by a 'crusty skin' on the top of the components. If its stuff like you get in the small 2 pack tubes then it may be ok, but no guarantees. If it is crusty, and i suspect it is, then mix it and chuck it away.
I have used some pretty old epoxy from tubes without issue, but it does degrade, so I'd probably not risk it. It also degrades through UV exposure as well as moisture absorbance, so if its in clear containers that will be a factor.
It can last, in a useable state, a remarkably long time. WEST has this to say:
"Storage and shelf life

With proper storage, WEST SYSTEM 105 Epoxy Resin and hardeners should remain usable for many years, especially if the containers are kept closed in order to prevent contamination. Over time, the resin will thicken slightly which, in turn, will require extra care when mixing.

Both resin and hardeners should be stored at room temperature. Indeed, if the resin freezes and thaws out many times it can cause crystallisation. If this happens, however, it is a simple matter to dissolve the crystals by warming the resin to 50°C and stirring for a while."

Have a read of this page if you are not entirely convinced:
Bear in mind that we call it all epoxy, but there are various different formulations out there which may have different storage characteristics. If you can check the manufacturer's spec that would be best.
You state that you did some fibreglassing 8 to 10 years ago? Is it epoxy or polyester?
They are not the same. If its polyester chuck it as by now its way past its sell by date & liable to not work.
As far as epoxies go they have a shelf life, I have used a lot of West & SP systems products & the hardener seems to go off before the resin, it goes dark brown & you get a pronounced ammonia smell, it still works but at possibly ten years old i would not trust it!
Some makes of epoxy the shelf life means what it says. I learnt this lesson the hard way on a customers boat, I had fitted a new skeg & rudder to a 28ft yacht made from fibreglass & the customer wanted the gelcoat epoxied to match the rest of the hull. I had half a gallon of epoxy tar left over from a job 2 years previously. "I will use that " I thought. So i mixed it up & painted it on. Conditions were warm & dry but it did not cure in fact a week later it still hadnt. I had to scrape the filthy half cured mess off & scrub it with gunwash to get the residue off before i could recoat with new stuff. It took a full day to clean that stuff off.
If in doubt mix a sample & test it first then you will know!

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