vermiculite granule size?

[rtnaw]

Hello,

This is my first posting. I live the Buffalo, New York area and am in the process of ordering vermiculite. Does the size of the granule matter? I have an option of large, medium, or fine. Thanks for any help you can give me.

Rob

[dmun]

I would think the coarser the better, since you are trying to get air spaces between the concrete matrix. Also, the big chunks might be less dusty.

Be sure it's the agricultural vermiculite, not silicone treated for use in domestic insulation. The silicone makes it hard to combine into insulating concrete.

[nissanneill]

Hi Rob, I have just poured my foundation and topped it with 100mm vermiculite which was graded as "#3 exfoliated vermiculite". It says on the 6Kg bags that it is for horticulture and insulation and the company seels heaps of it to people such as us for our ovens.
A picture of the mix is on; fornobravo.com/forum/f8/neills-pompeii-1-a-2005.html
It was mixed between 5 and 6 : 1 with portland cement and has set off nicely over the past week

Neill