36" Pompeii low-dome in Livermore, CA

[Larry P]

It was supposed to rain here today but it came overnight. Now I think we're in the clear for a while. I plan to take down the canopy on Saturday morning, mount the chimney plate, and maybe mount the chimney. Burn and do yard work Saturday and Sunday, and then start insulating and shaping the igloo with perlcrete Monday and Tuesday.

[JRPizza]

Please post lots of pics, especially when you start to cover your insulation.

[Larry P]

Indeed I will. I was just reviewing Les' and Russell's builds. Still not sure if I want to from the perlcrete dome with rebar & mesh or use a form. I'm leaning towards the former, but still deciding.

[Larry P]

This is what it's looking like now, 29.5" radius, hemispherical outer dome:

[JRPizza]

Have you checked out what Gulf did?
https://picasaweb.google.com/1101595...CPP5z4nqgsGFNg

[Larry P]

If someone says their oven has "no" cracks anywhere then they rank right up there with politicians and used car salemen........LOL it is the nature of the beast!

I'm not too worried about the crack. You actually need a magnifying glass to see it. I told my wife and at first she freaked, then she went to look for it, and then told me I'm an idiot.

[Larry P]

Have you checked out what Gulf did?
https://picasaweb.google.com/1101595...CPP5z4nqgsGFNg

I did. Mind-boggling attention to detail. I'm still considering that approach. I think the rotating form will give me a better shape, but the rebar/lathe form I can probably do in a day. The question is, can I get the rebar form into the shape I want? If I think I can, then I'd prefer to go that route. The other reason I like the rebar cage, is that I'll sink the rebar into concrete, which makes me feel a little better that I'll be able to resist minor shaking.

[JRPizza]

I agree that starting with a round base should increase the odds of getting a round end product, but until I play with some of the vermicrete I am not sure if perfectly round to start is going to help me
I'm hoping to try to emulate Gulf's dome finish, either with brick or tile. Not to take away from anybody's build, but if you are going with an igloo, you might as well copy as much as you can from Gulf and UtahBeehiver.

[UtahBeehiver]

Copy away, it is the highest level of flattery. High ratio V or P crete is tricky to work with, it is crumbly and can be hard to form. Both Gulf and I needed a solid substrate to lay our final covering on, IE brick slices for Gulf, something to screw copper shingle into for me. I did make a curved trowel to help form and hold in place my P-crete until it was self holding. Having a relatively round shape to begin with makes the process easier. Both you and JR enjoy the curing ride. The hard work is paying off now.

[Larry P]

I'm planning to do 10:1 perlcrete (already have 12 cu. ft. coarse perlite) so that's bound to be a 10:1 sobs to laughter ratio. And I have 4 10' pieces of 3/8" rebar. I'll probably start by bending the rebar around a form and see if that looks round enough to be a starting point.

Last night's fire was much better controlled than the previous night. I had the dome at a pretty solid 650ºF for several hours, the soldiers around 500, and the floor a steady 400. The dome did not start to clear again. This is probably where I should have been on Wednesday, but yes this is not exactly precision work.

I'll try to push it a little hotter tonight, then do a long hot burn tomorrow. I've got my sourdough starter out of the fridge and bubbling away, pizza it's been too long! Dough tonight with a 48-hour ferment will have me ready for pie on Sunday!

[UtahBeehiver]

Believe it or not, there is a unique smell when the dome starts to clear, kind of hard to explain, but see if you can smell it. Both Gulf and I swear there is a smell when the dome clears, not sure if it is the carbon burning off or our vivid imagination............

[david s]

I'm planning to do 10:1 perlcrete (already have 12 cu. ft. coarse perlite) so that's bound to be a 10:1 sobs to laughter ratio. And I have 4 10' pieces of 3/8" rebar. I'll probably start by bending the rebar around a form and see if that looks round enough to be a starting point.

Last night's fire was much better controlled than the previous night. I had the dome at a pretty solid 650ºF for several hours, the soldiers around 500, and the floor a steady 400. The dome did not start to clear again. This is probably where I should have been on Wednesday, but yes this is not exactly precision work.

I'll try to push it a little hotter tonight, then do a long hot burn tomorrow. I've got my sourdough starter out of the fridge and bubbling away, pizza it's been too long! Dough tonight with a 48-hour ferment will have me ready for pie on Sunday!

I believe the secret of doing a 10:1 vermicrete layer is in getting the mix right and the method of application. I've found that a 50/50 mix of vermiculite and perlite makes a more workable mix than using either of them alone. This is probably because you end up with a variation of grain size. I've tried both fine, medium and coarse grain sizes and found it doesn't matter that much although the fine stuff seems to require more water. I now use medium grade perlite and medium grade vermiculite. It may depend on where and how the stuff is processed but the correct amount of water addition is essential. For every 10 parts of aggregate (5 parts vermiculite, 5 parts perlite) I add 1 part cement and add 3 parts water. To make the mix more workable I also find a handful of powdered clay makes a big difference. So my brew is 10 Litres aggregate, 1 litre cement, 1 handful clay and 3 litres water. I mix the stuff dry first then add the water. Making up batches like this works pretty well. You may want to double the amounts to make bigger batches, but ensure all ingredients are mixed really well. Forget a mixer to do this as it just seems to stick to the mixer paddles and sides too much, also the grains tend to abrade and you start losing volume if mixed too much. I've found it much better to mix in a barrow or 20 litre bucket.If there is water pooling on the bottom of the bucket or barrow add a little more dry material.

When applying the mix, I always do it by hand, but always use rubber gloves when mixing and applying this stuff or you will regret not doing so. Starting from the base I less and hold for a few seconds making sure there is a horizontal top to the layer so the next level has something to sit on. Once you reach a point where the dome begins to lean in the application becomes much easier. To finish off I tap the outside of the layer with the flat of my trowel or a piece of 4x2 timber. This will give you a surprisingly even surface and by viewing the profile by eye, a very even spherical form.

I've vermicreted many ovens using this method and continue to do so. Remember that the vermicrete layer contains LOTS of water and anything thicker than 2" will take a lot of drying out because the moisture is trapped deep in the layer. It may appear dry on the surface after a couple of days but won't be deeper in. If you want a thicker layer i recommend allowing the first layer to dry for a week and then apply more. All your vermicrete layer does though is to produce a firm enough layer to act as a substrate to render against. I usually only use one layer around 35 mm thick.

Hope this (or some of it) is helpful.

[Larry P]

Thanks David. Very helpful.

[JRPizza]

Yes David, very timely! I spent some time poking around your posts trying to find your advice for doing the p/v-crete layer, so thanks for summarizing. Do you have any works of wisdom for what you have found works best between the insulation and the p/v-crete. Chicken wire, 1/4 inch hardware cloth, etc?????

[david s]

I don't use anything as chicken wire takes hours to cover the blanket and tie in. 10:1 vermicrete is not at all strong and the chicken wire really only serves to hold the blanket in place. Provided you get the blanket fitting neatly I can't see any other advantage in covering it with chicken wire. I just vermicrete straight on to the blanket.