tacky epoxy

Submitted byfrankp onThu, 06/07/2018 - 18:35
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Kayak Building

Anyone had epoxy over carbon fiber harden and then get tacky again?

I used the same batch of epoxy on my coaming (CF over ply) and my deck and it all hardened fine.  Then I flipped the kayak over to work on the skeg and the epoxy around the coaming got tacky again overnight.  2 days later it hasn't hardened again.  Any ideas?

frankp

I've never even heard of this happening. Is it possibly just blush - if you scrub the surface with water and a scotchbrite does the tacky layer come off leaving hard epoxy underneath?

Maybe a safer first test would be to scrape a small area and see if there is a hard surface underneath.

Justin

I can't really do any tests on the boat right now so I'm not sure.  This is the second layer so it's entirely possible that's what it is.  It has also been very humid here so I'm hoping you're right.  

FrankP

I had the same thing happen on a carbon coming, it also yellowed slightly.  I let it sit for a couple of weeks and scraped it off and then sanded it a bit to get more residue off.  I scrubbed and washed it and the next  epoxy coating was fine, I also did it on a humid day and the layer of epoxy underneath was still slightly tacky when I put it on.

 

If it feels like a sticky coating on top of the hardened epoxy, it is likely  blush. You should be able to scrub it off.

Yes blush is just part of the curing process.  Some epoxies are more prone to blush and some environmental factors can make it more likely.  

 

Blush happens on curing epoxy, so it can happen on any coat of epoxy. It happens if there is humidity during the curing stage. The curing stage last for several day.

Thanks for the feedback.  I was on travel for a week and took the boat out today to sit in the sun.  The blush is a bit better but still some there... I'll let it sit in the sun as much as possible this weekend to hopefully help it out a bit.  If not, I'll wash it down and see if that fixes it all.

frank

Thanks.  I was going to clean it anyway and I need to sand down a couple of rough spots in the CF prior to varnishing.  I figure between the two I should be okay.

frankp

JayBabina

Mon, 06/18/2018 - 18:01

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Always wash your epoxy coat. I always wet sand before varnishing even if its not tacky. Varnish will not dry or harden with blush under it. (the voice of experience)

What a mess -  cleaning off sticky varnish.