ORIGINAL: lodomjr
Dave,
I'm not sure what you have available in Australia, but you want something to seal the wood that is lite. With the resin thin the balsa will absorb some of the resin and causing the addition of extra weight. I'm hoping Dean, Mike or someone can chime in with other sudjestions where you live or give other ideas. Maybe clear dope or something like that, but not sure if that's the best idea.
Larry
Nitrate dope, thinned 50:50. Penetrates, seals and adds extremely low weight. Must wait 2 days for the thinner to fully flash and the surface is ready for epoxy or other. Go to the Composite Fabrication and Repair section. Look up Finishing with Carbon Veil
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MattK