Floor insulation options because of a lack of materials

[brickie in oz]

Here is a list of different things.
Thermal Conductivity of some common Materials and Gases

[Lburou]

All sand is not equal as an insulator

If you must resort to 'sand', choose a coarse, highly washed sand, a sand without the smaller particles that would tend to fill the air spaces between the granules. The coarse sand will allow more air space for trapped air like texassourdough pointed out.

[wotavidone]

G'day Joaam. Apologies for the late reply.

My ideas about using scoria came form this academic paper.
http://www.academicjournals.org/ijps...ep/Hossain.pdf

When you read it, you must first understand all the abbreviations. e.g. SA = scoria aggregate. GA=gravel aggregate etc. Also, one part discusses using scoria in cement as a pozzalan. The other part discusses using scoria as the aggregate in concrete. Cement and concrete are not interchangeable terms. That is, when you read it, you must remember that cement is the gray powder used to "glue" the aggregates (sand and rocks) together to make the solid mass we call concrete.
This is what I would have used for the insulated base of an oven if I had not already bought 200 Litres of coarse vermiculite, as it still concerns me a bit that vermicrete has "adequate" compressive strength and lowi tensile strength, while this scoria concrete has good structural strength all round.
Hope this makes your choices easier, not harder.
Regards,
Mick

[wotavidone]

P.S. The paper talks in kg/m3 for all the ingredients. But at least he also lists the bulk densities so that you can convert to volumes. Unfortunately, this works out at about 3 scoria, 2 sand and 3 cement by volume for mix B-1, and 4 scoria, 2 sand, 3 cement by volume for mix B-3. Very approximately, using a Bulk Density of 1.51 for portland cement.
That's a lot more cement than used in a standard 3 gravel, 2 sand, 1 cement concrete mix.

Having said that, I would personally just get myself some 20mm scoria, some clean washed concreting sand, some portland cement and make a test slab of 3 scoria, 2 sand, 1 or 1.5 cement by volume, with just enough water to make it just wet enough to lay (remember after you have added enough water to facilitate the chemical reactions, the more excess water, the weaker the concrete).
Then I'd let it cure for a week under plastic. The I'd hit it with a hammer, and call it strong enough if it didn't break.
But that's just me - for all of my scientific background, I still reckon results on the ground are more useful data than academic papers and theoretical calculations.

[Lburou]

You could always make a hearth like GianniFocaccia did (pictured below). Then, just fill the depression with scoria -or combination of sand and scoria- then, put your firebricks on top of the that. While not an optimal insulation layer, it would provide some trapped air for insulation and eliminate the cement issues you are struggling with. I'm still optimistic that you will find some form of vermiculite