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?

strange catalytic reaction with 30 minute epoxy
 

That's scary! I've seen 30 minute Z-Epoxy 'kick' after 5 minutes when it was mixed with Milled Fiberglass or Microballoons!

Jerry

strange catalytic reaction with 30 minute epoxy
 

Could be really hot with 3 oz. in a cup???? It has been suggested elsewhere to use a shallow container so the heat can't build up as easily and speed the curing. I have had this happen with just a little more hardener, but the cup has been very hot. Was it????

strange catalytic reaction with 30 minute epoxy
 

I'm not sure what happened to you, but the one time I tried mixing as much as 3oz of epoxy, it got very hot very quickly (actually smoking), and within minutes it was solid rock.

That's why I use epoxy resin for glassing wings. It's made to be mixed in large quantities and stay liquid for a long time.

strange catalytic reaction with 30 minute epoxy
 

when using and mixing epoxy use old MAN magazines or whatever,mix a couple differen't spots on a page then tear off and throw away,go to the next page.This is a good way to use all those mags that are no longer any good that are just lying around.

strange catalytic reaction with 30 minute epoxy
 

Instead of tearing up your old magazines (which means storing them until needed) I use Post-It notes. If you're not mixing great honking amounts, they work great. Stick the adhesive side down on your mixing hand side and it never goes anywhere, no matter how vigorously you mix. You have just enough space to mix the right amount of 5-Minute without wasting any, and they are easily disposed of. If you want to get really fancy, buy one of those dispensers. It works just like a Kleenex box and it's re-fillable.

Ed

strange catalytic reaction with 30 minute epoxy
 

I mix my epoxy on a board covered with smooth Formica and clean it with alcohol before it cures, was late once and still got it off with a scraper.

catalytic reaction
 

Pinball: you may have hit on the problem, too much epoxy mixed at one time would generate more heat as it set and might accelerate the curing process. I did not notice it getting hot until the moment it "kicked" and turned yellow, but I was not holding the cup so it may have. The cup I used was a shallow cup.

Thanks everyone, I would have never thought that quantity could be the issue.

strange catalytic reaction with 30 minute epoxy
 

I mix my epoxy on a plastic lid that my wife saves for me from the two pound coffee cans. She asked me once if she could help me with my models & I told her to save lids for me, probably have over 200 now & don`t have the guts to stop her!! Just flex the lids & the hardened epoxy pops off & you can use it over again for next batch. My wife is now saving bread wrapper ties for me now, wish I could remember what for??>>big max 1935

strange catalytic reaction with 30 minute epoxy
 

Hi I also have had larger amounts cause a faster cure rate ! I since never mix much more than 1/2- 3/4 oz in one container. I use the paper pad mixing pallet for smaller amounts. But the 1oz epoxy cups for my larger amounts I clean and reuse the cups ! I clean the cups as quikly as possible with rubbing alcohal !or if it cure I pop it out. But the cups are cheep if your working on a large glue job and want fast mix and managable. I think the last batch of 50 was around $2 at our LHS . Just not expencive enought to break anyones bank!! also the cups have graduation marks in fractions of OZ or in CC .. just my $.02

strange catalytic reaction with 30 minute epoxy
 

Yep, happened to me with finishing epoxy... while I was applying to fiberglass already laid on the airplane. Damn!!! Got hot, smoked, and became hard in less time than I could remove it all from the plane. Quantity was indeed the issue (I was mixing a full 3 oz. medicine cup).

- George