Unfinished Composite Question

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Tiger Tim

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What should the surface feel like on an unpainted mouldless composite airframe? I ask because years ago I was offered an unfinished Dragonfly and one of the reasons I passed it up was because it felt tacky to the touch. I’ve always wondered if that was a sign of improper resin hardening or if that was just something you wash off as part of building the thing.
 
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Vigilant1

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Some epoxies form an amine blush on the surface, particularly if it cures in humid conditions. It feels waxy or tacky. It is harmless and washes off with a little elbow grease.

So, it could have been that, or something more serious. A rag, soapy water, and a rinse would tell ya if it was a serious issue or not.
 
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Voidhawk9

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Sounds like maybe it wasn't fully cured yet? It can take a few weeks for thin laminates to properly cure (and they can cure further with heat - the post-cure), and of course that time can vary widely depending on the resin used.

Yes, amine blush is also another possibility.
 

Tiger Tim

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Some epoxies form an amine blush on the surface, particularly if it cures on humid conditions. It feels waxy or tacky. It is harmless and washes off with a little elbow grease.
Sounds like that may have been it. The airframe was made in Florida so the humid bit checks out.

Sounds like maybe it wasn't fully cured yet? It can take a few weeks for thin laminates to properly cure (and they can cure further with heat - the post-cure), and of course that time can vary widely depending on the resin used.
This Dragonfly was essentially a long-abandoned project that had changed hands among airplane people a bunch of times, always as part of a lot and never the main event, it seemed. I had figured the work was at least a decade old so if it hadn’t cured by then it wasn’t going to. Too bad I didn’t know about amine blush at the time (or really prior to just now), maybe I’d be ripping around in a weird little tandem today.
 

berridos

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Strange that epoxy feels tacky. Looks like a failed cure or improper mixture proportions.
In polyester its frequent, and should receive a parafine treatment to avoid that tackiness.
 
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