Thread: Build Log light weight project
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Old Nov 29, 2012, 09:36 AM
quincross is offline
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Ride, Surf, Fly, Sleep
Joined Dec 2007
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Originally Posted by G_T View Post
Just note that thinning epoxy with alcohol greatly reduces its strength, and extends the cure time, often requiring heat to reach full cure (if it ever does). Just FYI.
Flat out at work at present, but couldn't resist replying on an area in DLGs where I don't feel like a newbie!

Gotta go with Gerald on this as an ex-Composites R&D guy - but it doesn't weaken it much if you use it correctly and not enough to cause an issue in this application.

I've not used West being in the UK, but any proper laminating resin will be OK.

Personally, I'd go with a slow 60min hardner and then heat the resin (as you can't heat the foam without melting it). This will cause the resin to cure much faster and it will go very, very thin. This way you get strength and save cash on thinners.

Also, I'm not sure about modern epoxy systems but the destructive tests we did on aerospace resins circa 2001 show that slow hardeners increased the strength of the matrix compared to the faster systems. I can't remember the exact figures but it was by quite a significant amount. The chemistry showed that slow systems gave more time for longer molecules to form and polyform branching in the molecules was increased - basically think of spagetti; with slow hardners the strands of spagetti where longer and more intertwined/closer hence them making it more difficult for them to slide past each other.

Finally, If you are using thinners, make sure they're foam friendly - i.e. not acetone!

The other thing is note that the 30min or 60min hardners are rated for "pot life", i.e. how long you can work it. Not for cure time. This can be up to 10 x longer in a thin film (i.e. cure overnight to be safe with stressed parts). Also make sure you know whether the system mix ratio is by volume or mass (most are mass).

(PS. You'll love the FF - definitely go with D47's all round, also called SD100's etc, I have and they're an excellent compromise as a newbie myself, see the build in the thread)
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