strange catalytic reaction with 30 minute epoxy
This has happened to me on two planes in the last 3 months: while joining wing halves (in both cases it was a Yellow 60 size), I was spreading the 30 minute epoxy using an epoxy brush. Everything was fine, the epoxy was still very fluid, I was only 5 minutes into it.
Note: the H9 epoxy was carefully measured and mixed, was fresh, and the same bottles had been used to make several other batches without a problem.
Then as I applied some epoxy to the inside of the wing joiner hole with the brush, the epoxy in that spot became instantly thick. Before I realized what had happened, I had dipped the brush back in the epoxy cup and all the epoxy in the cup (about 3 oz) started to cure immediately, turned yellow, and within 30 seconds it became thick. I quickly removed the thickened epoxy from the joiner hole, mixed some more and finished the wing. The epoxy that had been applied before this happened was fine, so its not a problem with the batch itself.
Is seems like some residue in the joiner hole caused a reaction in the epoxy that accelerated the curing process. When I transferred that to the cup by dipping the brush, it affected that also.
Any ideas?