Mixing Insulating Concrete

[KasinH]

Re: Mixing Insulating Concrete

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.

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.

[Neil2]

Re: Mixing Insulating Concrete

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.

[dmun]

Re: Mixing Insulating Concrete

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.

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]

Re: Mixing Insulating Concrete

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

[leemc]

Re: Mixing Insulating Concrete

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.

[david s]

Re: Mixing Insulating Concrete

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.

[david s]

Re: Mixing Insulating Concrete

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.

[jrparks]

Re: Mixing Insulating Concrete

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.

[Lill Dave]

Re: Mixing Insulating Concrete

Using this insulating concrete mix over a insulating blanket and wire mesh how do you think it would hold up on a portable oven, cracking wise.

[SpringJim]

Re: Mixing Insulating Concrete

As for mixing for a vermicrete or perlcrete layer over a dome I have no experience. I used insulating blanket and then dry, loose filled vermiculite. I suspect one would have to mix like you did in order to get a stiffer material that would better stand on itself.

Wiley

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.

[Wiley]

Re: Mixing Insulating Concrete

SpringJim has it right, one really needs a mixer attachment for a drill in order to use the slurry method. And using the attachment one can achieve a better ratio of cement to vermiculite or perlite too.

I don't know how one could make the slurry without the mixer attachment, maybe slow pouring the dry cement into a bucket of water and stirring like crazy with some sort of paddle while mixing. Even using the mixer arrangement when mixing the cement in the bucket (before adding to the wheel barrow of dry or moistened vermiculite) one has to move fairly quickly...stop mixing, pull drill mixing attachment from bucket and pour the bucket in one smooth motion. No stopping to chat or a smoke or to scratch where it itches as the cement settles fairly quickly. Once poured the mixer attachment goes in the wheel barrow to mix the vermiculite and slurry. Then it's a dip of the bucket into the wheel barrow load of mix and pour into the form. All in all it goes quickly.

As for mixing for a vermicrete or perlcrete layer over a dome I have no experience. I used insulating blanket and then dry, loose filled vermiculite. I suspect one would have to mix like you did in order to get a stiffer material that would better stand on itself.

Wiley

[SpringJim]

Re: Mixing Insulating Concrete

Lee the video is good...it's pretty weird stuff! I agree with the general description that it looks like oatmeal or is even like trying to mix styrofoam beads with water initially!

I did Craig's slurry method and was very happy. I only used a small amount of portland in the water which created a very light mixture for me. The portland was well mixed into the final product because it was part of the wet side of the formula. (much better in my opinion than dry mixing) I did use a paint/drywall mixer attachment on the portable drill and this worked well.

For later insulation layers I went with some fireclay too, just to make the mix a little more manageable for the dome insulation. I'd suggest that you can reduce the portland content if you use the slurry method and that will give you better insulating values.

I think one mistake I made was to use siliconized perlite for masonry insulation which made it harder to mix with the liquid...but it finally worked.

Thanks

[leemc]

Re: Mixing Insulating Concrete

The trouble I had with making a slurry was that I don't think I had right tool for it - which would be a mixing attachment for the drill. When I did it I just poured half a bucket of cement and started putting water in it. This resulted in the cement at the bottom of the bucket to become like gumbo clay and I had a real difficult time getting it into the mix. If I had a mixer or maybe tried to do it it two batches or maybe putting water in the bucket first and adding the dry cement to it probably would have gone much smoother.

The other method I used - pouring the dry cement into the perlite, mixing, adding water and mixing was pretty easy. Working with this stuff is child's play compared to mixing real concrete.

If you want to see some pictures of how I formed my recess for the insulating concrete you can go here....

http://www.fornobravo.com/forum/f21/florida-igloo-5702.html

Lee

[Wiley]

Re: Mixing Insulating Concrete

Good looking video, I like your enclosed area for the insulation under the hearth, almost a basin to hold the under hearth insulation.

On my WFO I did the slurry mix and found that I could get a ratio of 9 or 10 to 1 vermiculite to cement ratio. Honestly after viewing your video I think the dry mixing followed by adding water requires much more physical work than the slurry method. Also in support of the slurry method, it allows for alot of self leveling of the mix (as it is quite fluid when first poured), that's good if your forms are level, not so much if they are not. Simply dip and pour the mix from a wheel barrow by a bucket.

When mine was cured it had the consistancy of cork...I had to dig out the corners and fill with concrete... the same corners you previously had cast as part of your "basin". I wasn't clever enough to have thought that part thru at the time I was building. Hopefully someone will alter the plans so that one isn't directed to cast the entire layer as insulation. I think a square basin with lopped off corners like yours or a true octagon would be best. But what do I know? I've only built one oven although at a Christmas Party yesterday I was approached by a friends wife who would like a oven and wanted me to assist her husband building one this coming summer.

Wiley

[dmun]

Re: Mixing Insulating Concrete

Your video looks good: it's weird stuff but you seem to have it right. You report that the slurry method doesn't work? I thought that was the new method that avoided the clumping at the bottom of the pan, never tried it myself.

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