Just thought I would throw this out there as it saved me a lot of money. I had 3 new/old stock (never opened) packages of 5 minute epoxy and some 30 minute epoxy that I used one time. The epoxy part of the mix was hardened on all of them and I thought they had gone bad. I was getting ready to throw them away when I opened the cupboard and saw the crystalized honey on the shelf. I took all the epoxy bottles and put them in some water in a pan on the stove. Warmed it up slowly on med heat and you know what happened. All the epoxy turned back crystal clear and so I tried to mix some up and it worked just as new epoxy would. I didn't realize that the epoxy can crystalize like honey does. I had thought I put the hardener lid on the epoxy and ruined it but I guess not.

John, Microwave oven works too. Just remember to loosen,or remove the caps, and keep an eye on it, so that you don't melt the bottles. If this is the epoxy you are using for the cowl, there are much better resins for that application. Most of our "hobby" epoxies are chemically NOT a 1 to 1 mix. They are probably something like a 4 to 1, or a 5 to 1 mix. To make the measuring chore easier for the end user, the manufacturers put fillers in the hardener. The fillers have to be a liquid, that gets hard when cured. Some times those fillers solidify over time, but can be re-liquefied with heat. Greg.

Be careful when doing this. The #1 cause of this crystallization is moisture. Although it appears to have cured properly it most likely has greatly reduced strength. Depending on the application it may not be an issue but then again it might be.

Epoxy resin will never go bad in a sealed container. Over time, it will revert back to its original - solid state. I place the bottle in the microwave for ten seconds with the cap off. You are good to go. Just be careful not to cook it. I am a Mercury Adhesives dealer and have been using this practice for several years without failure. Hope this helps.