Rnning Dog,

Instead of vermiculite, have you ever used perlite or even aerolite (the white foam BBs)? They would seem to be more stable in that they don't decompose and are light to boot.

Jerry

The Swedish always seem to do it right-IKEA,Volvo,so it stands to reason that they would come up with a way to use waste wood products.
But...you can do lightweight with as stated perlite(comes in many grades,I use cryogenic which is very small pellets,almost sand sized).You don't need organics in your mix at all.I saw a vendor at a gift show last year that ONLY uses perlite for his fountains,and was charging a good dollar for them!
Cheers from here

I've been using the large perilite. Do you find the small grain better or stronger? Do you just use cement and cryogenic without the peat?
Thanks

Large grain perlite cement is quite weak. I haven't been able to improve this with sand, but it is possible that fibre admix would help. By comparison with foamed concrete, large air pockets (big perlite balls) are a weak flaw while tiny air bubbles (cryogenic perlite) are like a free way to reduce weight without losing strength.

I've used the extra-fine perlite with white Portland and been very pleased. It seems to be quite strong (only time will tell, got those test pieces outside all winter) and makes a blindingly white crete.

It is very "floaty" stuff. You should use eye & breathing protection as it would be very easy to breathe it in.

I got a huge bag from a masonry supply house for about $15. It weighs hardly anything, and that's coming from a wimp...

I've used it now for almost a year and have found the teeny,tiny perlite beads to be just fine.I use a cement/sand/perlite(1:1:2) as my standard for masks and outdoor fountain parts and the mix is stable,easy to work,and sets up real purty.
Like it has been stated,protect yourself.The dust from these materials can get you good.And permanent!
Cheers from here