Early planning questions

[CSWolffe]

I have a couple of odd questions about home built ovens that I cannot seem to figure out on my own or on this site. please help me in my ignorance.
First, what exactly is 'fireclay' and where would be a good source? Masonry dealers or ceramic stores? When tracking down refractory cement(homedepot does not carry here) the counter help at a masonry dealer gave me an odd look when I asked him about it.
Second, how do the insulatory properties of vermiculite and 5/1 insulating concrete differ? Sub question, does the insulating concrete have any structural strength? Am I better off with four inches of vermiculite with a two inch concrete shell, or six inches of insulating concrete? I would of course cover either with a protective layer of stucco, and either method would include reinforcing metal mesh.

[maver]

Fireclay is usually sold as a fine powder and can be obtained from most masonry suppliers. When wet, it feels like clay you would use for pottery. It has alumina and silica in sufficient quantity to facilitate heat transfer and thereby reduces hot spots in your mortar which makes it more heat tolerant.

Refractory cement is hard to find and reportedly expensive. Few builders here have used it, choosing instead a proprietary refractory mortar or using mason's lime (different than gardener's lime, mason's lime is also available in masonry supply stores) to achieve a heat tolerant mortar. Mason's lime is slower to set and not as strong as regular cement, but if the cement fails with time, the lime is a backup.

Loose vermiculite or perlite is a slightly better insulator than perlcrete or vermiculcrete, but the difference is not substantial. If you buy an insulating concrete product rather than make yourself, it may have different insulating properties and may have different structural properties as well (look for johnrbek's excellent dome build write up for a use of insulating concrete). If you are making an igloo oven there is no need for an exterior concrete shell over the insulating concrete or vermiculcrete - just stucco right over it.

[CSWolffe]

Thanks, that was helpfull, exactly the information I needed.

[Dutchoven]

As an added note to the great advice. When I asked about refractory mortar I also got the strange look. I used a proprietary mix of portland, mason's sand fireclay and hydrated lime to build my oven( 1/3/1/1 mixture). I have however since found that Superior Clay Corp dealers will usually have some type of premixed refractory mortar available. Here in the Memphis area they have something called Firerock(I think he called it that). And it is actually quite affordable although more expensive thatn mixing your own. Some building inspectors might require it if you are installing indoors.
Best
Dutch