Insulation - Rock salt and sand

[Xabia Jim]

I was talking with a spanish bulder/friend and he mentioned that before modern insulation materials like Arlita they used a mixture of sand (or crushed rock) and rock salt (gravel sized) for the insulating materials for their ovens.....interesting!

I know there was some discussions about possibly using salt in constuction and found his reference worth mentioning here.

Jim

[edschmidt]

Hello jim,
Im confused about using sand. I have read others talking about using sand as an insulation, but to me it doesnt make sence. In my thinking insulation means air and lots of it, therefore the less weight per cubic foot the better the insulator right? The reason I am particularly interested is that when I built my oven I used 4" of sand under my firebricks with the intention of it functioning as a heat retention layer since its not much different weight wise per cubic foot (or meter in spain) as cement. If I have any problem with hearth temp its with it being to hot. I have 7" of depth in the dome and I have to mop the hearth a lot to stop pizza, bread or roasts from burning on the bottom.

Sooooooooo, which is it, is sand an insulator or a heat sink.

P.S. Jim when are you coming back to michigan? Let me know and Ill make sure to make plenty of dough for pizza's.

P.P.S. its about 20 deg. here

[Xabia Jim]

I think sand by itself would be a heat sink. My read in this discussion was that it filled the matrix between the larger salt gravel. So I think it was mainly salt and a little crushed stone to keep the whole mass solid.

I do actually think that for this use they were building bread and roasting ovens so thermal mass would have been more important than insulation. (Did they even understand insulation 50 years ago? Seemed like we built stud houses with open air spaces right up to the 70's....)

....back in a week

[maver]

Air is not the only heat insulator, although it is a good one. Ultimately insulation ability has to do with heat transfer, and there is an engineering term that addresses this called K value. I looked the K value up for sand once - there is some variability as there are many types of sand. Sand is not abysmal as an insulator, but certainly not as good as the modern insulations suggested in the pompeii plans.