vermiculite Tools, Tips and Techniques Discuss vermiculite in the Pizza Oven Design and Installation forums; I recently called a masonry supply house to see if they carried vermiculite. They said that the vermiculite I need ...

[mrgweeto]

I recently called a masonry supply house to see if they carried vermiculite. They said that the vermiculite I need is called "attic vermiculite" which is bigger in size than the standard (plant and garden) vermiculite that they and other home centers carry. Is this true and also when mixing with portland cement that I need to add sand so the finished insulated pad will not crumble. Need some info please. Does the portland cement that a Home Depot or Lowes carries have sand already mixed in (premix Quickrete). Am pouring the hearth tomorrow and would like to get my supplies ASAP. Also how much vermiculite is needed per bag.
G

[dmun]

They said that the vermiculite I need is called "attic vermiculite" which is bigger in size than the standard (plant and garden) vermiculite that they and other home centers carry.

No. This domestic insulation vermiculite is treated with silicone to prevent it from absorbing water, and doesn't mix with the portland well. You need regular agricultural vermiculite. Particle size doesn't matter.

when mixing with portland cement that I need to add sand so the finished insulated pad will not crumble

No! No! No! the vermiculite is the only aggregate in insulating concrete! Sand is not an insulator, and this won't work at all.

Does the portland cement that a Home Depot or Lowes carries have sand already mixed in (premix Quickrete)

No! Two different things. You want portland cement, not concrete or mortar mix. Portland is the active ingredent in concrete, and you're making concrete with a lightweight aggregate, instead of sand and gravel.

[mrgweeto]

Great advice. I really appreciate the info. I was a little suspect when I got off the phone with the person from masonry supplies and you have certainly made it all clear. There is a large grower in the area that I know and I am going to hit him up for the vermiculite. It will be a pizza trade for vermiculite deal if I'm lucky (haha).
Thanks again and hopefully I can get through with the hearth pour tommorrow and think about laying out the insulating pour soon after it cures.
G