Good stuff. Water-based is the go. Too much petrol in product gives a head ache without the night out.
http://avesstudio.com/ - I've used it for some board repairs. A gnarly polymer of dough-like consistency. You can buy it @ sculpting shops in AU. Or ship order it from those guys directly to where ever. Even though board will be far from sustainable design still, it will be hell durable.
Also there are soy based urethanes, heaps of them come from insulation industries:
http://www.biobased.net/products/index.php
http://www.hgtvpro.com/hpro/nws_ind_nws_trends/article/0,,HPRO_26519_3679395,00.html
http://www.envirofoaminsulation.com/faq.html
Would avoid spraying perhaps. Liquid form is better to my liking.
There is also hempcrete:
http://en.wikipedia.org/wiki/Hempcrete
But yeah, for answers, I think we might need to look into food (e.g. prawn chips for foam) and health (e.g. dentistry) industries. I found building industry to be a dodgehouse, producing and selling too many products which should not be on the shelves.
On bamboo:
http://www.google.com.au/url?sa=t&source=web&ct=res&cd=3&url=http%3A%2F%2Fbambus.rwth-aachen.de%2Feng%2FPDF-Files%2FMechanical%2520properties%2520of%2520bamboo.pdf&ei=WIJ1Sp-ROI2uswPSq7TtCA&usg=AFQjCNFNtPj3wkWeTIovPhSMSOildh-NeQ&sig2=p6BXCBiiYDIi46Ic3vMu6A
I reckon go thickest you can go, but no thicker. Been mulling over this idea for some time. It would be uber to actually surf one
Good luck and cant wait to see the result!!!