Medium vs Fine grade Vermiculite?

[aeu99217]

Hi,

I've been reading up on the insulation hearth and as far as i can tell no-one has asked this question, but apoligies if has laready been crossed.

For making the insulation hearth, which grade of vermiculite is best, fine or medium?

Here's the link to the shop im going to buy them from ScotPlantsDirect|Perlite and Vermiculite| Orders £49.99 and Over Free Delivery - Growing Needs - Perlite / Vermiculite

Many thanks for any help

Cheers Ross

[Les]

I would go with the medium. During my build, I needed one more bag and it ended up being the fine stuff; think sawdust. (was in the same package, just a different store). I think when it is mixed with the Portland, it will not have as good as insulation as the coarser product.

Les...

[aeu99217]

Nice one, cheers Les.

Also, your oven looks a peach!

Cheers Ross

[kebwi]

The larger particles will insulate better. You don't really want dense cement in there, it's just glue to hold the vermiculite in a solid, so the bigger the vermiculite chunks are, the tougher time heat will have diffusing through the insulation.

[Rolaed]

I live in metro Detroit area and need to know where to find vermiculite? Thanks in advance.

[aeu99217]

Hi Rolaed,

I couldn't tell you anywhere in specific, but here in Scotland it was dead easy to get a hold of. It is used in gardens so most decent gardening stores sell it. It is also on amazon (in the UK).

Cheers Ross

[aeu99217]

Also, thanks for the advice Kebwi

[david s]

The density of vermiculite seems to be the same whether it is fine medium or coarse, so theoretically it should make no difference to the insulation value. I had to switch to using fine grade when I couldn't get the coarser stuff, but I found that it makes a more consistent end product (less prone to crumble away) and easier to apply, so now I use the fine stuff all the time. But try it yourself and make up your own mind.

[aeu99217]

Thanks David. I've ordered a 100 litre bag of medium grade to use for the insulating hearth. I'll maybe buy a bag of fine stuff for the igloo.

Cheers Ross

[Rolaed]

I finally found a local store that sells it(garden supplies place). I guess Vermiculite is used in gardening too.

Question to all:

On the hearth slab, I have heard two stories. First you put Vermiculite and then on top the cement. Or visa versa, first the cement and then the vermiculite. How deep should each layer be?

Same for the dome. Put the vermiculite on first and then the cement/stucco coat?