Yet another insulation question

[wotavidone]

Don't want to start an epic saga on the pros and cons of each, but I can get perlite or vermiculite at exactly the same price. Both are coarse grade hydroponics growing media for $44 per 100L bag delivered. So the choice simply comes down to which one is best.
Experienced oven builders - if you were standing in the shop with perlite to the left and vermiculite to the right, which one would you go home with?
Regards
Mick

[dmun]

They're both the same. Same insulating properties, same manufacturing processes (they are expanded minerals - popped in heat like popcorn).

Perlite is white: it makes a good visual marker when your gray portland is evenly distributed.

Vermiculite is said to be less dusty.

Neither one of these is a deal killer in my book.

[Neil2]

I used half perlite and half vermiculite. I found this a bit easier to work with that straight vermiculite, particularly when forming/screeding the dome layer.

[benguilford]

Originally Posted by dmun

They're both the same. Same insulating properties, same manufacturing processes

Hi dmun,

Do Perlite and Vermiculite actually have the same insulating properties?

Forgive the question, I'm just a natural-born-fool from Gippsland, but the data I have indicates that Perlite has a thermal conductivity almost half that of Vermiculite (0.031W/m.K for Perlite, 0.058W/m.K for Vermiculite).

[wotavidone]

I hope you are correct Ben, because I have a few issues with the other materials I might use, and I was thinking life would be a lot easier if I could get away with a 3.5 inch layer under my floor.
If perlite has only half the thermal conductivity, then maybe I can do it.
Its all to do with readily available steel sizes for the steel stand I think I'll build.

[Ken524]

I suspect there are a lot of variables involved with Perlite/Vermiculite/Portland insulation value. Grain size, ratio of Portland, how long it's mixed, etc.

For our purposes (insulating under an oven floor), 4" of either material will give you satisfactory results. Is one better than another in a laboratory? Probably. Are you going to notice a difference in your oven. I seriously doubt it.

It's like comparing flat panel TV's at Walmart. One might look a little better in the store, but either will look great in your living room.

[lt4827]

Thank you Ken for that analysis. For our needs, there is no reason to re-invent the wheel.

[david s]

Ben,
Last time I checked thermal conductivity it said perlite was just a slightly better insulator than vermiculite, not double. I prefer to use vermiculite because it seems to mix up better and hasn't got that irritating dust that perlite seems to have. The perlite I use tends to abrade more than the vermiculite on mixing and you end up losing a bit of volume. You are not meant to mix either of them for too long, i think for this reason. Vermiculite also seems to coat with the cement a bit better, the grains of perlite are rounder and smoother and it doesn't seem to stick as well. Sorry for the extended answer. If I were making a choice between the two I'd take vermiculite.

[Johnny the oven man]

For under floor insulation, you cant beat calcium aluminate board, end of story.
OOPs that should be Cal. Silicate board.

[benguilford]

Thanks for your response Ken and David, and don't worry, I like extended answers!