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Throw Deep 03-27-2008 08:50 AM

Igloo style dome insulation
Thanks for all of you who helped me get my dome up, cured and ready for my son who was home from the war on his 3 week R&R. We had a grand time with him...made pizza twice without the benefit of a chimney (read much smoke in face). Now he's back in Bagdad :( and I'm back to finishing at a more leisurely pace...learning along the way that I can make the oven hot but I’m a novice at actually making pizza. The learning curve on sour dough starter is steeper than building a dome out of brick...that's for certain!:D

Speaking of thanking heaven, I know there was divine involvement in my dome since there are no cracks (except a few little hairline ones in the concrete skim coat). I saw a little steam in the 4th or 5th cure when my fire got away from me and consumed my wood on one side that was supposed to be drying out for a subsequest cure. But there was no repeat of smoke or steam on any of the following I think I'm out of the woods (fingers crossed).

My handy dandy temperature gauge says that I'm getting brick surface temps over 1,000 degrees F at the top of the dome and on the floor in front of the coals. My thermocouples are saying my bricks are getting above 600 degrees in the dome and 500+ in the floor. Should those temps come on up toward the 1,000 degree mark also before I start cooking? I have not gotten there yet. My sourdough pizzas are cooking in about 4-5 minutes rather than the 2 minute pizza I'm shooting for. Perhaps it takes a little time for every little bit of moisture to cure out and that's keeping the bricks from absorbing more heat?:confused:

The chimney is up and I am ready to turn my attention to applying the vermiculite/portland insulating cement to the blankets on the dome.

If the weather holds, on Saturday I’ll put on the last insulating blanket and apply the insulating concrete to plaster the blankets into place and create rigidity for the insulation. I’ll put water proof stucco over the insulating concrete to finish it when it is dry enough?

But here's my real question for the to keep the dome shape symmetrical…i.e. how to keep the depth even all around as I apply the 3” of insulating concrete on top of 3” of blankets? My eye is not that good! Got any ideas on how to reference my depth as I go?

Also, if you have any experience with the insulating concrete being used on the dome…how long should I let the insulating concrete dry before I put the stucco finish on? While it should not get particularly hot due to the blankets being between it and the thermal mass of the dome, it will be wet initially and I don’t like the idea of trapping all of that water under the stucco.



dmun 03-27-2008 04:11 PM

Re: Igloo style dome insulation
I didn't build a igloo enclosure - and I think most people who do did it freehand. You could cut a plywood jig with the correct radius, but I think you are going to find that just getting the perlcrete up onto the dome is going to be an effort in itsself. You can even out any dimples in the dome when you get to the stucco layer, that stuff is sticky and you have more control over it.

And my thoughts go out to your son in Bagdad. Yikes. Sounds bad over there this week.

james 03-27-2008 04:22 PM

Re: Igloo style dome insulation
Bob, it sounds to me as though you haven't had the holy %^@&$%^# fire yet. You should be able to easily hit the 800ºF mark -- which will get you that 90 second - two minute pizza. Keep upping the size of your fires, and you'll get there.

You can "build" an Igloo enclosure if you want. You can use pencil rebar and lathe, and bend/shape it all until you get the shape you want. Then you do the scratch coat and finish coat against that structure. Or, you can build up from the dome and insulation to get the Igloo shape. They both work.

I'm always pleased when I hear about families doing their oven project together. What a great way to spend time together. We can all look forward to you all cooking pizzas again.


Throw Deep 03-27-2008 05:37 PM

Re: Igloo style dome insulation
Sounds like I'll just have to "free hand" the shape of the igloo...wish me luck.

Also, I'll see what a few more red oak logs on the fire do for the temperature.


asudavew 03-27-2008 06:42 PM

Re: Igloo style dome insulation
My understanding (limited of course) is that you might want more insulation at the apex of the dome... Most heat loss will occur there, so you might want more at the peak!

It's not so important what it looks like, hang on to the heat at any cost!


cvdukes 03-27-2008 07:16 PM

Re: Igloo style dome insulation
You could glue little depth guides at stragetic spots around the dome and cover with the insulating concrete until they are covered. I would use a stiff wire (like coat hangers) and bend the bottom into a little circle that would form a large enough base to hot-glue to the dome.

RTflorida 03-27-2008 08:15 PM

Re: Igloo style dome insulation
I used a wire coat hanger as my depth gauge, but not in the manner described; I merely put a piece of duct tape on the wire (at the 4" mark) and "poaked" it into the perlcrete at various points as I slopped it on.

the freehand approach is not as difficult as it get a feel for applying it pretty quickly, and as mentioned, any peaks and valleys can easily be addressed with you final render. Biggest thing to remember is to start at the base of the dome and work up, the chicken wire DOES help keep it in place as you pack it on.


gjbingham 03-27-2008 08:46 PM

Re: Igloo style dome insulation
My experiences - the less spherical you put the blankets on the dome, the more work you have to do to get it back to symetrical. I didn't do exceptionally well, but I can live with mine.

I wouldn't worry about the cure of the vermiculite too much. A week should be plenty. It will still be wet inside (I think it would still be moist a month later, based on my experience of cutting my vermicucrete insulation later 6 weeks after placing it), but the base coat of the stucco will help suck the extra moisture right out of it. Give that base coat a week or 10 days to cure/dry before placing a waterproof finish coat. CJim - disagree if you think otherwise. I'm winging it a bit.

Before going to the stucco though, you can always add more chicken wire/lathe to uneven areas and add more vermicucrete to get you back to round. Trust your eyes. Stand WAY back and walk around the dome. Irregularities are quickly obvious if you pay attention. Also, if you can find a vantage point from above, a ladder or roof, so that you can look down on top of the dome, you'll pick up minor problems that need work.

Hope that helps a bit.

david s 03-28-2008 02:25 AM

Re: Igloo style dome insulation
I don't think coathanger wire is a good idea, its too thick and provides a path for heat to escape to the outside. I use thin wire about 0.5 mm twisted together with aloop at one end and some legs to sit flat against your dome. This is held in place by a layer of concrete and these wire ties act as depth guages for your vermiculite layer and as anchors for your mesh for your ferro cement outer shell. Works a treat.

Throw Deep 03-28-2008 05:18 AM

Re: Igloo style dome insulation
Thanks for all of the great ideas on shaping the dome. At this point my blankets are on and the chicken wire has been shaped around it...not anchored in any way to the dome itself. So it is a floating shell around the blankets tucked in on the front between the blankets and the back and sides of the chimney. It is tight enough in some places where it won't move but in others there is an inch or so between the wire and the top blanket. I don't think that packing on the vermicu-crete is going to move it. Hopefully that will be okay.

I think I might cut a straight piece of coat hanger wire and try to see if it will penetrate the blankets and seat against the dome for a depth guage. Perhaps the 3" blanket layer will hold them in place while I put the vermicu-crete on. If not, I'll do the walk around eyeballing method.

So, once I get the vermicu-crete on there, I'll let it cure for a week or so and then let the scratch coat of the stucco do the same. I don't suppose that fires during that curing period will have any impact one way or another?



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