Mixing Insulating Concrete

[jrparks]

Great video! I wish I had seen it before I started my WFO. I think it will help new builder get a good understanding of the process. When I made mine, I mixed the cement and perlite (5:1) dry in a 5gal bucket, about 2/3 full, with the lid on and shaking. It worked well. I then mixed in the water same as in the video, using a wheel barrel and hoe.

[david s]

I think the secret is getting the correct amount of water into the mix. If you put too much water in, the cement slurry sits on the bottom and you are left with a weak mix of aggreate (vermiculite) on the top. I mix it dry with cement then add water 3 Litres for every 10 Litres of vermiculite.It seems like it is too dry because it doesn't flow like normal concrete , but it works well.

[david s]

Sorry I should have added here that the 10:1 vermiculite, cement mix is for dome insulation. For the hearth you need a 4:1 for some more strength.

[leemc]

Lildave

I think using a blanket under the perlite is a bad idea. It will probably compress loosing a lot of its insulation value and likely cause a structural failure of the oven above it. Better to stick with perlite or FB board if the thickness is a concern.

You could use a blanket on the sides though with perlite over it. That's what I did in my oven - you just don't want weight bearing on it.

[ThisOldGarageNJ]

I mixed mine 6-1 dry in a cement mixer, let it stir for a few minutes, then added as much water as i needed.. (this was put on top of 2 inches of insulation)I cooked in my oven for 6 hours with a fire yesterday and there was still snow on the roof this morning..

Cheers
Mark

[dmun]

Just to clairify Leemc's post: Using a blanket covered by vermiculite is not good between the floor and support slab. That's a pretty standard finish over the dome if you're doing the igloo style.

Originally Posted by leemc

Lildave

I think using a blanket under the perlite is a bad idea. It will probably compress loosing a lot of its insulation value and likely cause a structural failure of the oven above it. Better to stick with perlite or FB board if the thickness is a concern.

You could use a blanket on the sides though with perlite over it. That's what I did in my oven - you just don't want weight bearing on it.

[Neil2]

Using my concrete mixer, I found the vermiculite particles were breaking down, producing a denser = less insulating material. I eventually mixed it gently in a wheel barrow. I used 5:1 for under the hearth and 12:1 for the dome insulation layer.

[KasinH]

I'm wondering if someone could put, say, crushed stone, rocks, seashells, etc. over that perlite/cement finish you're showing in the first picture instead of the bricks you're showing in the second picture?

KasinH.

Originally Posted by SpringJim

I covered my whole dome with it and it worked fine for me. Started at the bottom and built it up in a thick layer. I did have an initial layer of used firebricks which I'm sure helped as it gave me a terraced effect. I did add a small amount of fireclay which I believe improved the workability. I cut some of the layer off with a handsaw for my entrance and it was a lot like styrofoam, fragile but it floated too! I had a very high perliteortland ratio.