insulation tips

[cobblerdave]

G'day Chaz
What are fire blankets ?
Regards dave

[chas]

Never actually got one out of its container Dave - but over here (over there most likely too) they're the emergency square of  Kevlar or something similar kept folded up into a container fixed by stoves in catering kitchens and labs using open flame. You chuck 'em over a flare-up. I cleared a restaurant and kitchen as part of a refurb and kept all sorts of likely stuff in case it came in handy...
I figured that if I sewed fire blanket material inside my canvas 'cap' it would isolate it from the heat of the dome and help with insulation. The cap could stay on during oven use rather than just as weather proofing in down time. 
But it would be useful to know what temperature the outside of a dome reaches. As fire blankets are made for smothering rather than insulation, they may transmit heat and result in a touch of spontaneous combustion. 

Chas

[moonhead]

Hi Chas, your dome in use use will internally reach temperatures exceeding 800F. This will permeate to the outer face of the brickwork albeit not to the same extent but it will get extremely hot. 3" of the Vermicrete you have put underneath the hearth, also applied to the outer surface if the dome would provide insulation to the dome to some extent at not to great a cost.
Rick

[cobblerdave]

G'day
Moon head your very right there .
I've used my own oven without the insulation layer to burn out the ply dome form. Added heaps more wood and accidently made some pizza along the way. Used a ton if wood cooled down real fast and the outside was positively dangerously hot . Woundnt have kids around one.
Pearlite, verciulite is cheap and available and will take the high temps. Aluminium foil, space blankets, domestic insulation have all been tried but fail because these are really high temps were talking about here. Twice as high as a domestic oven, you cannot hold your hand in a WFO oven at pizza temps. No Way
Regards dave

[chas]

Thanks, as ever - and as I don't want my beanie to explode in a shower of sparks, a slathering of vermicrete it is then. Or. as I'm using lime putty, maybe that should be vermilimp.

Cheers,

Chas

[cobblerdave]

G'day
Portland cement is usually used because it set quickly. Lime doesn't . Yes of course cement tends to break down at higher temps but its only the top couple of mm is effected the rest is protected by the pearlite and holds the top lot in place.
Be warned they don't call it the devils porridge for nothing. Its a real sh!t to apply. Mix by hand in small batches pick up a handful land press carefully on building from the bottom up. No playing or smooth the stuff just lump by lump till you get to the top.
5 pearlite 1 Portland for under the hearth, 8 or 10 to 1 on the dome.
Regards dave

[thebadger]

Hello,

Is there a way i can not use a fireblanket and just use Verciulite?

Am i right in thinking you mix the verciulite with concrete and spread it over a blanket and chicken wire?

[downunderdave]

Apr 4, 2016 14:52:43 GMT thebadger said:

Hello,

Is there a way i can not use a fireblanket and just use Verciulite?

Am i right in thinking you mix the verciulite with concrete and spread it over a blanket and chicken wire?

Not quite sure what you are planning here. If you are not using ceramic blanket why would you then spread it on the blanket? You can dispense with the blanket altogether and just use vermicrete, but as it takes up around a third of its volume in water, there is a lot to eliminate. I've found doing it in layers of around an inch and a half, with a week of drying in between works ok. For every 10 parts vermiculite add 1 part cement powder and 3 litres of water. This makes up a pretty workable mix that is also very insulating. Making the mix richer (adding more cement) reduces the insulating capacity drastically. I also find adding a handful of clay for every 10 litres of vermiculite helps to make the mix more workable.