Fillets are sticky

[Jeremiah Johnson]

I used some West Systems 105 / 205 epoxy with 406 microfibers over the weekend to put some small fillets on a Semroc kit. I use the pumps so I always assume I have the correct mixture of resin / hardner. I mix the resin / hardner and let sit for 20 minutes and then put in the microfibers a pinch at a time until I got toothpaste thickness. I was just hoping for a little bigger fillet than what I get with glue.

Taking a close look tonight and I see that 6 of the 8 fillets are great but 2 are still sticky. It seems that I must not have gotten enough hardner – perhaps I’m pump challenged (although, I’ve not had this trouble before).

What do I do? Do I mix another batch and put it over the stick, brush on some hardner, heat the area, or scrape the existing fillet off and put on a new batch?

[AdrianParticipant]

I’d recommend scraping the bad ones and starting over. My guess is that it isn’t a bad ratio, but rather insufficient mixing. The rule of thumb I’ve been told is “If you think you’ve probably mixed enough, you’re about half done.”

[Chris LaPanse]

What kind of temperatures have they been in?

If it is anything <70ish, I would keep them in a 70-85 degree area for another day or 2 and see if they harden up. If they don't, then I would go with Adrian's advice.

[Jeremiah Johnson]

The rockets stay in a room that is about 65 F. I’ll keep this one somewhere warmer for a day and see how it looks tomorrow.

Thanks for the advice guys.

[Warren B. MusselmanModerator]

I’ve had this happen with West Systems myself, again due to insufficient mixing. I usually mix for at least 60 seconds and I really work to get all the corners and crannies of my container well stirred up.

When it happens, I try to remove as much as I can – usually by wiping things down with acetone. If you can’t get all of it that way, you can try heat setting the remainder by heating it up to around 120 – 130 degrees for an hour or two. I’ve used my wife’s oven on warm and then leaving the oven door open a bit. That should do it.

Warren

[Anonymous]

The fresh-laid glass was very sticky on my 4″ minimum diameter project. I was quite concerned. I let the works sit in the garage on a hot summer day, and that took care of a lot of it, but not all the tackiness was gone. I then determined I’d try the acetone thing, which (for me) did not work. In the course of rubbing the acetone into the finish, some of the rag I was using got caught up in the glass. After a day or two I used a garden hose to clean off the rag fibers.

Incredibly, whatever happened with the hose and water did the trick. As far as I can tell, there is exactly zero reason that the tackiness went away due to the water. That said, it DID go away and I flew the rocket on a full M and the fins are still on there. Weird.

My advice is to try heat (65 deg F is not enough), then try acetone, but I’d try the water thing, too. As noted, there is no chemical reason this should work — but it did in my case. Strange.

[Warren B. MusselmanModerator]

In that case, the stickiness isn’t uncured resin, but something called Amine Blush. A sticky, waxy-ish coating that occurs sometimes on epoxy cured below normal temps or in high humidity. Harmless and should come off with a good scrubbing of soap and water.

Warren

[Ken PlattnerParticipant]

Use a green scrubby and mild soapy water.

[Anonymous]

I wouldn’t do ANYTHING until I tried to let it cure in warmer temps. Heat lamp, perhaps?

It is minus 6 (with gusts to 43mph) in Iowa tonight. No epoxy will cure in my garage tonight 😯 Spring seems like a L-O-N-G ways away!

[SCOTT EVANS]

I wouldn’t do ANYTHING until I tried to let it cure in warmer temps. Heat lamp, perhaps?

It is minus 6 (with gusts to 43mph) in Iowa tonight. No epoxy will cure in my garage tonight 😯 Spring seems like a L-O-N-G ways away!

You keep that weather there!!!!

We have a balmy 15 degree low with 20mph winds!
Much nicer here! 😉

[Author]

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