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Puy de Dome 07-03-2008 11:25 AM

Vermiculite/vermicrete; its nature and application

First off, I have read about 'vermicrete' on FB, and am wondering if that is what you guys mean by a mixture of vermiculite and cement and water?

If so, I have a question or two about vermicrete. If I were to describe this stuff, at least that wot I have made, I would say it is akin to ricicles/rice krispies when soaked. It's a bit mulchy.

When applying it for the first coat on chicken wire, it's not terribly easy - the chichen wire is strung over a ceramic blanket and there are various largeish holes to fill underneath the wire. Does this sound about right?

Does it dry solid? Should it remain friable and crumbly when dry? Is it fragile?

My main query is how waterproof is or should be, this layer of vermicrete? Indeed, any subsequent layers? I have currently covered over my work in case of rain.

When done with this insulation layer, I'll be putting on a render of mortar. How thick should that be? I take it that that will be waterproof?

If I'm wrong about this thing you call 'vermicrete', what is the uk equivalent please?

Many many thanks


nissanneill 07-03-2008 06:45 PM

Re: Vermiculite/vermicrete; its nature and application
Hi PdD,
vermiculite concrete as the forum guys/gals call it, is quite fifficult as I found out.
However, with that said, I found an easy way to apply it over the chicken wire laid over the themal wool blanket.
Read and check out the pics at my postings which show and explain all the ins and outs of the process at:


RTflorida 07-03-2008 10:03 PM

Re: Vermiculite/vermicrete; its nature and application
answers in order:



not really, it stays together if left alone and has enough compression strength to support the oven but is quite fragile - it will gouge and bits will break off if you too rough on it.

not waterproof at all....if it gets wet it will get soggy all over again. Your render depends on whether you go igloo style or with an enclosure (house type). If you go igloo - you have a couple of options 1) finish with stucco which should give you great weather resistance or 2) top it with type N or Type S mortar (both are weather resistant) and finish with brick, stone, tile (I did mosaic). Follow the stucco manufacture's recommendations for the thickness of the coats.....if using the N or S mortar - 1/2" will do.

Do check out Neil's link


SpringJim 07-04-2008 04:06 AM

Re: Vermiculite/vermicrete; its nature and application
I used perlite and the CVdukes method of mixing. I got a very high ratio of pelite to portland...about 1/2 bag of portland to two bags perlite.

It definately has a wierd consistency (oatmeal with rice krispies?) and set's up like styrofoam initially. The more portland used, the higher the strength.

I was worried about compressibility but have almost finished the dome and it has held up fine.

Next challenge is using the perlite mortar when I cover the dome with insulating firebrick.....will probably make pouring the hearth look easy!

I will add that I've wet down the insulation layer as I've laid my bricks without an apparent problem getting it wet.

Puy de Dome 07-04-2008 11:55 AM

Re: Vermiculite/vermicrete; its nature and application
Thanks for the replies everyone.

I spent the best part of today doing the vermicrete layer. Not easy to get it on the sides. I sort flung the stuff at the mesh and hoped it stuck. It's certainly thicker on the top of the oven. About three inches - and that's on top of a one inch ceramic blanket.

It's not easy stuff to work with by any means. I'm hoping that the final two layers of render/stucco will be easier.


havefun 04-22-2009 06:13 AM

Re: Vermiculite/vermicrete; its nature and application
well reading all the posts on vericrete am not happy using it at all reasons 1: not robust enough 2: if am going to have to render it on top then what's the point? the rendering WILL get hot b4 the vervicrete stops any more heat loss 3: i don't like having bits of foamy stuff when am cooking in a close space (the clay oven) so for that i be using thermalite blocks lay my fire bricks on top n then some reinforcments n concrete or screeding to get everything level with the fire bricks

more permanent more robust n No foam bits mixed with cement giving off eventually low fumes flavouring my food in the clay oven at first i thought it was a mixure that after been mixed will form to something like thermalite blocks.

thx guys Regards all Takis

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