Confused about vermiculite as a base.

[caspian]

I already have a base that is 4" concrete with mesh. I am going to build an igloo WFO on it. My question is, is the vermiculite/portland mixture strong enough to build the WFO on top of?

Since my base is about 4' x 4', it would be easiest to build a frame around the perimeter and pour 4" of a vermiculite (i would assume with a wire mesh), then build the round igloo on top of that. Will that work?

If not, there would be MUCH more work involved.

thanks

[david s]

Re: Confused about vermiculite as a base.

The answer to your first Q. is yes. A 5:1 vermicrete slab is plenty strong enough in compression.
For vermicrete over the dome the usual method is to make up a weaker mix say 10:1 because strength is not required here, but just strong enough so you can render against it. The problem is the water removal. I like to to do it in 1" layers leaving a week between each so it can dry. This means easier water removal when it's finished. Creating some kind of mesh wrapping to contain dry vermicrete sounds difficult but may be doable. The other alternative is to build a doghouse or enclosure around the oven and fill it with loose vermiculite or perlite.

[Wiley]

Re: Confused about vermiculite as a base.

Caspian, I would suggest you consider only making the vermiculite layer as large as needed to support the oven and insulation layers. As you mention you are going with a dome (as opposed to building a small house) for the WFO, having the extra vermiculite beyond what is needed is potentially going to cause you problems with keeping the weather (read that as water/rain ) out of the oven. There is no need for the insulation beyond the diameter of the insulation you are placing over the dome. The stuff is a great insulator but also a great sponge, absorbing water quicker and releasing it slower than most of us would wish.

I haven't looked at the plans to see if they have been updated but originally they wanted a complete layer across the support slab. Wasteful IMHO and problematic regarding water intrusion.

Hope this helps,
Wiley

[david s]

Re: Confused about vermiculite as a base.

Caps ian,
Sorry, I think I may have misinterpreted your question. I thought the second question related to vermicrete over your dome. There is not much point in using mesh in the vermicrete under floor layer as the stuff is not particularly strong and mesh would not do much to strengthen it. As Wiley suggests you do not need to extend the vermicrete to the edge of the supporting slab. Just take it out an inch or so bigger than the outside of the inner dome.

[caspian]

Re: Confused about vermiculite as a base.

If I plan on finishing the top of the exposed vermiculite with marble will I be ok with regard to water penetration? I really want to avoid doing this in two steps (two forms)

Thanks
Caspian

[david s]

Re: Confused about vermiculite as a base.

Yes you can, but it is a good idea to leave the vermiculite exposed after laying it. There is plenty of water contained in it for hydration without having to keep it damp for a week. Allowing the sun and wind (provided there is some) to help dry the layer for a couple of weeks before building over it is a good idea IMO. If you can't do this then at least leave the edges exposed so moisture can escape there. You can seal up the edges when you're happy that sufficient water has been removed.

[Les]

Re: Confused about vermiculite as a base.

Caspian,

Mable on top would work. My concern would be that some marble is pourous and in your environment, might be a bad thing for the marble. I got talked out of using granite for that very reason.

[caspian]

Re: Confused about vermiculite as a base.

very good point. there are plenty of good looking porcelan (sp?) tiles that i can go with.

Caspian,

Mable on top would work. My concern would be that some marble is pourous and in your environment, might be a bad thing for the marble. I got talked out of using granite for that very reason.