Shaping vermiculite concrete dome

[Terracotta dome]

Re: Shaping vermiculite concrete dome

I applied mine the same way that David did his, using rubber gloves and had fun playing in the mud.

[dottavio]

Re: Shaping vermiculite concrete dome

Definitely eyeball it. You will be able to see any gross imperfections and correct them. The minor imperfections will add to the character of your hand built brick oven. Think of them as your artistic signature

Doug O

[neophyteguy]

Re: Shaping vermiculite concrete dome

Thank for the heads up David! This step was confusing me and I haven't even received my Casa yet.....

[jmadison]

Re: Shaping vermiculite concrete dome

THANK YOU David ...makes perfect sense. I am determined to get this right, thinking theres not going to be much of a 'do-over' space

[david s]

Re: Shaping vermiculite concrete dome

You don't have to do a vermicrete layer over the blanket, but it evens out all the lumps and bumps where the blanket overlaps and folds. Your outer rendered shell would otherwise be overly thick to get back to a nice hemispherical form. Your common sense tells you the mix is too crumbly and it won't set, but wait 24 hrs and it will. Not really strong, but good enough to render up against. Adding more cement just reduces the insulation value.

[jmadison]

Re: Shaping vermiculite concrete dome

Here's the rank beginner's question ... the install instructions on my modular kit say to wrap the insulation banket, cover in wire and then the finish coat ... NOTHING about a layer of vermiculite concrete???

[Gulf]

Re: Shaping vermiculite concrete dome

Here is the screed I used for shaping the vermicrete layer (12:1 mix):

Neil2,
That's it!! I've been wondering where I got the idea for my template . I scoured builds for a couple of years before taking the plunge. I know that I read yours start to finish, as I did many others, only making mental notes.
Thanks Neil.

[Neil2]

Re: Shaping vermiculite concrete dome

Here is the screed I used for shaping the vermicrete layer (12:1 mix):

[lwood]

Re: Shaping vermiculite concrete dome

The most important value is missing, the "R" value. Hundreds of ovens have been successfully built on top of the 7 or 8:1 mix, as long as it is properly supported. The dome certainly is not structural. The vermicrete will crumble to the touch 24 hrs after. So be careful when you remove your forms. I gave it 3 or 4 days before messing with it. It firms up nicely and proceed. It's structural properties are not a concern here, insulation is the issue....the more the better.

[rjdealhome]

Re: Shaping vermiculite concrete dome

I came across this thread while looking for information on using vermiculite concrete as a basecoat for stucco on my dome, and thought I would pass on this chart that I found on the Schundler Vermiculite Concrete site. It may be useful for those wondering (as I did) about different mixes and relative strength.

[david s]

Re: Shaping vermiculite concrete dome

It should be firm in 24 hrs. You'll be able to easily crumble it away, but all you need is a surface that is sufficiently strong enough to render/stucco on to. Dry it out well before doing this though.

[clg763]

Re: Shaping vermiculite concrete dome

How soon does the mixture start to cure? How much should I try to compact the mixture with my hands? So far I have seen very little signs of curing, I am used to concrete no longer being workable after less than an hour.

[david s]

Re: Shaping vermiculite concrete dome

I find mixing 10 parts vermiculite to 1 part cement (by volume) dry, then adding 3 parts water and mixing it with my hands in a large (20 litre) bucket works pretty well. Replacing the vermiculite portion with 50% vermiculite and 50% perlite improves the workability of the mix.

[clg763]

Re: Shaping vermiculite concrete dome

Ok, I have begun putting the vermiculite concrete on the dome using a 10:1 ratio, I am having a very hard time getting the cement to set up though.

I started off with a 3:1 ratio of water to cement for the slurry, then poured this over my vermiculite and mixed this by hand. The mixture did not have the feel of good concrete, it was still very crumbly despite all the moisture and nothing I could do seemed to help the texture. I just sort of set a course of a few inches around the dome but the mixture was a fairly loose pack and I don't feel good about it. Now, almost two hours later, the mixture has not set at all. I have never seen concrete do this, what am I doing wrong?

[david s]

Re: Shaping vermiculite concrete dome

I place the vermicrete with my hands, one handful at a time, starting from the bottom of the dome work all the way around with one hand on the outside and then one on top to create a ledge for the next row. I press and hold for about two seconds and it stays really well, but you need to get the mix just right. If you have water sitting in the bottom of your mixing bucket then you've added slightly too much water. When you've placed the vermicrete over the whole dome you can tap the surface with the face of a trowel lightly to get a perfect hemisphere.