Vermiculite Vs Perlite

Posted by Rado (211.29.202.37) on October 17, 2004 at 19:58:19:

In Reply to: Vermiculite Vs Perlite posted by August V on October 17, 2004 at 12:16:14:

August, perlite is a volcanic material, to get it light in weight and to use it as insulation industry heats it up quickly (i think to temperature 1600F - somewhere under 900C) to expand it a few times, like popcorn, at this time it turns to white color. As it expands it looses water and the granules create many tiny air bubbles, this sealed air gives it great insulating properties.

It is manufactured to several grades from 2 lb/Ft3 (32kg/m3) to 11 lb/Ft3 (180kg/m3) bulk density (loose weight), granule sizes 4-8 mesh# and finer, get sieve number 4 (5mm). Perlite softens in higher temperatures and becomes more heat conductive. It is cheaper used mainly as aggregate in building to lower the concrete floor weight of tall buildings or to insulate house walls, roofs, decks, as chimney linings, etc. (temperature or sound-noise control too). It's perfect for loose-fill insulation between masonry. As refractory insulation it's being used at service temperatures somewhere up to 1800F (just under 1000deg.C, not reachable in wood fired ovens ;o) heaps by metal melting industries e.g. in castables they use right on the surface of melting metal as back-up heat insulation layer for backing higher duty dense refractory material. It's also used as aggregate in Portland, or at least it used to be, that's why this cement is already a bit refractory.

It will work between dome and outside skins so if you can buy it cheaper go for it. Although some grades are a bit more absorbing it won't matter in wood oven, it will do the job well as loose in a sealed fill. (Vermiculite bulk density: 4-10 lb/Ft3 (64-160kg/m3) and thermal conductivity: 0.40-0.45 Btu in/sq ft deg.F (0.058 - 0.068 W/mk) I have a book somewhere on perlite concrete-s, when I get back home I could look in it if you needed.

Ed and Heidi can be proud of the oven they built, actually I only have seen picture of the work in progress and it looked very nice! Hope you'll email me a photo of your oven too. Thank you.