Does epoxy and hardener have a shelf

life?The stuff I’m using is a year old.

I glued some plywood together with blocks for boat sections 2 weeks ago and when I stessed them while assembling they pulled apart with little wood loss. I reglued one immediately and the epoxy left over kicked and hardened. I must have mixed it incorrectlythe first time , but that isn’t likely.

I’m wondering the same thing
I have a little repair kit that the maker of two of my boats sent me, and I never got around to making use of it last year. I HAVE kept the stuff in the refrigerator the whole time, figuring that would delay any degredation over time.

A couple years ago I was involved with some concrete testing at our local airport, and the epoxy the contracor used to glue steel dowels into existing concrete wasn’t setting up as fast as it was supposed to. They thought it might have been because the stuff was more than a year old. They go through several hundred gallons of that stuff a year, so they seldom have any old material on hand.

the pro boat builders in the area take care not to keep hardener around for more than a few months. On the other hand I used some hardener and resin left over from a project last July, I think and it seemed to work well. The keys for me have been mixing and temp during the set up period.

BTW- tried a trick a guy that works at Carolina gave me. I was helping a friend with a repair on a glass skiff. When it came to the application of the gel-coat I applied with a brush in a 12x24 inch area. Then when it was still wet I covered it with plastic wrap and rolled it out with a dry paint roller. Once set the plastic lifted right off and the gel coat was smooth and had no visible pin holes.


Mine has been good for several years…

– Last Updated: Apr-22-06 4:50 PM EST –

Usually I precoat each piece on bare wood, let dry and then do the lamination coat. Adding bonding fibers to the glue mix will do wonders. West calls it 403 Microfibers now..

Polyester resin has a much shorter life than epoxy...

Mine is Raka epoxy and I’m
beginning to think that I mixed it incorrectly.I just hope I don’t have to buy more plywood and recut six panels.

call the manufacturer
I’m pretty sure for wood applications it can be a few years old without problems. The hardener can darken significantly but the epoxy itself should be stronger than the wood. I think the major manufacturers will say that it should be used in less than a year in order for it to meet the published psi figures for breaking strength. Which is still many times greater than the wood.

For people building with glass/carbon etc. laminate where the cloth and resin are IT then it’s probably more critical than a s&g hull where the wood is a major structural element.

One of the things that happens in small batches with pumps is that the first pump can be inaccurate with a bubble in it. Also some small mixing containers can have indentations that hold unmixed resin if you don’t mix THOROUGHLY. Then there’s the problem of building in 70degree temps and later on doing something in 60degree temps and not realizing what a difference ten degrees can make in cure times if you move the glued piece too soon. It’s also possible a marginal mix in lower temps with old slow epoxy might take a few days for a full strength cure compared to new epoxy, ten degrees warmer, correct and THOROUGHLY mixed. The difference might be 24hrs or more from all those factors for the joint to be strong enough to be handled/unclamped.

It might have been …
Just starvation as the epoxy soaked in to uncoated wood… if that was what you did… The fibers I spoke of helps prevent stavation when laminating…

Good luck… GH

Forever and ever…
The System Three Epoxy Manual claims indefinite shelf life of their resin and hardener if stored in air-tight containers below 90 degrees farenheit.

I suggest contacting manufacturers for other brands.


West System
I’ve been using left over West System epoxy for 3 years now. Several years before that, someone refound their old epoxy and hardener while cleaning up their garage, and sent it back to Geougon Brothers who make West System eopxy. In their lab testing of 20 year old resin and hardener, it had degraded some and wasn’t good as new, but still was acceptable for most purposes.

A year, anyway
Last year I asked my local vendor, who sells System Three, if year-old epoxy was still good. He said it would last much, much longer than that.

He was right. I mixed it up and used it–no problems.

I have found West to work
indefinitely, though the hardener (205) gets dark and thicker with age. The pump still pushes it through, and the epoxy still hardens properly. However, the mix is a bit thicker, so if I am doing serious work, I stick to fresh West, so it wets the cloth out well. I save the old stuff for wood repairs. It has a dark reddish cast which matches mahogany and cherry rather well.

MAS Slow cure
I built a kayak 5 years ago and have been using the left over MAS Slow Cure ever since for bonding paddle tips,hull repairs,installing a bulkhead and other jobs around the house.

The hardener did get a little darker but it seems to work just fine.

IF I were building another boat I would use fresh stuff.


Epoxy shelf life
Basically - no shelf life. You can use if for years.

The proper way to do a wood to wood joint is to clean the surface which is to roughen it too. Mix your epoxy and coat both surfaces with un-thickened epoxy which allows it into the fine scratches and to penetrate the grain. Then mix some thickner to the rest of the batch and apply that to both surfaces and clamp together. You don’t want to over clamp like you do with carpenters glue. The epoxy is harder than wood so you don’t want to squeeze it dry.

The next day when it seems hard, it’s only hard to the touch. It takes a few days to get to it’s optimum strength. After a few days, you’ll need explosives to get it apart.

Know that cold certainly affects it.
Rather than risk bringing the stuff into the basement I left it in the garage over the winter…expensive mistake.

don’t worry, heat it up…
If epoxy is left in the cold it doesn’t degrade or chemically change, it just thickens. Put it in a microwave or, if it’s in a metal container, an oven at a low (@125 degrees F) temperature. It’ll soften up or become liquid again, and be good as new.

In general , epoxies have a long to permanent shelf life , and are much less moisture sensitive than polyester resins and (worst of all) urethanes, both of which have much shorter shelf lives, and are generally incompatible with water and moisture.

Most all have a shelf life
I work on airplanes for a living and we use a lot of different adhesives and sealants and they all have a shelf life. Some 3 months to 1 year. Of course we can inspect and update the shelf life but only by 1/2 of the original date, we can update it twice. Even the epoxy resin I bought at the RV shop had a shelf life. It list date of manufacture “12 months from date”.

Hope this helps


Marine Tex…
I had lost a previously opened can of Marine Tex which is a thickened epoxy for boat repairs…

I found it 15 years later and it worked just fine.