How to insulate a cast iron pizza oven.

[nth]

Hi,
I'm quite new in this forum, and my dream is to build a real wood fired oven in my back yard. In the mean time i've got a Lo Goustaou wood fired cast iron pizza oven, and I'm having a good time making pizza in it.

However, - I live in western Norway and when it's freezing outside and the wind is blowing it's difficult to keep the oven hot. The weight is just about 174 kilo, so there is not that much temperature storage in the oven.

So here's my question for you experts out there:
Is it possible to make a sort of removable "hat" to insulate it?
Like the one they use on the tea-pot?
It should be removable because I use the oven as a grill by removing the top of the dome.

I guess it's quite unusual, but it may be some material that could be formed as a sort of insulation hat.
Hope anybody can give me some tips about this!

[nth]

Re: How to insulate a cast iron pizza oven.

Here is the oven

[stonecutter]

Re: How to insulate a cast iron pizza oven.

Sure it's possible. Why not make an insulated box with removable top out of vermcrete or perlcrete.....similar to a foam box cooler.

Like this......




Mix at 6:1 ( Permiculite or Perlite : Portland )

[wotavidone]

Re: How to insulate a cast iron pizza oven.

What an interesting thing. I take it you can undo the three bolts and lift the dome off to use it as a grill? I've never seen one of these before, where did you get it?
Your question has reminded me of something.
A while ago, my company's analytical laboratory threw out an electric furnace.
Our scrap recycling guy pulled it apart to liberate the huge transformer for its copper windings.
The walls of the steel cabinet were filled with perlite that was held together with something.
I always wondered why I could get the thing to 960C without burning the paint off the outside.

I couldn't make up my mind what it was holding it together. Eventually I concluded that the mystery glue might be sodium silicate. Also referred to by our refractory contractors as "waterglass".
I've never tried it, but if you can get it, it might be worth an experiment.
It looked like it would have less thermal mass than perlcrete made with Portland cement, but I'm not sure of the relative strengths.

[nth]

Re: How to insulate a cast iron pizza oven.

Thank you, Stonecutter!
I have really no knowledge of this
Do you know if it's possible to make a sort of foam insulation (like the cooler) rather than of concrete? It would be a great advantage if it's removable. If you look at the picture it's possible to remove the two top layers (with the handles) to transfer the oven into a big grill.

[nth]

Re: How to insulate a cast iron pizza oven.

Wotavidone,
I got the oven here in Stavanger, Norway. It's french made, I think.

I don't have to undo the bolts, just lift up one layer after the next by the bolts. It's just stacked.
I could carry the whole thing piece by piece by myself from the car and just put it together behind the house.

I live 50 meters from the sea, and it's very easy for a few persons to split it up and transport the whole thing down to the shore.

Because of the grill function it would be nice to have a lightweight insulation that is easy removable.

[wotavidone]

Re: How to insulate a cast iron pizza oven.

The perlite held together with the mystery glue was certainly lightweight.
I suggest you remove the bolts, if possible, cover you oven with a layer of plastic cling-film, such as saran wrap or glad wrap, whatever it's called in Norway, as smoothly as possible.
Then apply a layer of perlcrete to a couple inches thick, casting a couple of shaped wire handles in it as you go.
When the perlcrete "tea-cosy" has set, lift it off by the cast in handles and remove the cling-film.
If you wanted to make it more robust, you could build up your perlcrete layer, let it dry, then put a thin outer layer of fibreglass on it. This assumes you get the insulation layer thick enough that the fibreglass shell doesn't melt.
This is the approach I'd use if I tried the waterglass as the binder, but I'd go at least 100mm thick.

[stonecutter]

Re: How to insulate a cast iron pizza oven.

Thank you, Stonecutter!
I have really no knowledge of this
Do you know if it's possible to make a sort of foam insulation (like the cooler) rather than of concrete? .

Perlite or vermiculite shouldn't be that difficult to find....try a nursery, horticulture center or building supply....Google local sources.

6:1 is referring to the ratio of each material, measured by volume...any size container will do according to your needs. So, a 6:1 mix design would contain 6 parts vericulite or perlite, and 1 part Portland cement ( not concrete mix, which contains large aggregate).

Foam will not hold up to the heat, and it will disintegrate or melt. You need something that has some thermal resistance, like vermcrete or perlcrete. It is cheap to make, easy to form, and most on this forum have successfully used it with no prior experience.

It would be a great advantage if it's removable. If you look at the picture it's possible to remove the two top layers (with the handles) to transfer the oven into a big grill

I've never had to build something like this, but here's an idea on how to make an insulated box.


What you can do, is make a a square form with another smaller form inside of it. Fill the cavity with your insulating mixture, packing it down as you go. I made a test panel during my most recent build, and it held up well. I even used it for a temporary door for a few months.

http://www.fornobravo.com/forum/21/m...x-19009-4.html

The previous page will give you an idea how to mix a vermcrete/perlcrete mix.

Your box could then be coated with an elastomeric paint, slurry of acrylic/portland etc...something that will be a bit more durable than the insulating mix...it holds together ok, especially when well packed, but it is still friable.

There is no reason you couldn't make the box in stackable segments, with a removable top either.

You should start a thread if you experiment with this. I'll help if I can, and I'm sure you'll get plenty of suggestions from the forum.

[nth]

Re: How to insulate a cast iron pizza oven.

Thank you so much!
Now I have to do my homework and read about perlite, vermiculite, perlcrete, vermcrete and whatsitsname.
I understand that it's a lot to learn about this subject!

[TropicalCoasting]

Re: How to insulate a cast iron pizza oven.

The perlite held together with the mystery glue was certainly lightweight.
I suggest you remove the bolts, if possible, cover you oven with a layer of plastic cling-film, such as saran wrap or glad wrap, whatever it's called in Norway, as smoothly as possible.
Then apply a layer of perlcrete to a couple inches thick, casting a couple of shaped wire handles in it as you go.
When the perlcrete "tea-cosy" has set, lift it off by the cast in handles and remove the cling-film.
If you wanted to make it more robust, you could build up your perlcrete layer, let it dry, then put a thin outer layer of fibreglass on it. This assumes you get the insulation layer thick enough that the fibreglass shell doesn't melt.
This is the approach I'd use if I tried the waterglass as the binder, but I'd go at least 100mm thick.

Sounds interesting.

Refractory use

Water glass is a useful binder of solids, such as vermiculite and perlite.
When blended with the aforementioned lightweight aggregates, water glass can be used to make hard, high-temperature insulation boards used for refractories, passive fire protection and high temperature insulations, such as moulded pipe insulation applications.
When mixed with finely divided mineral powders, such as vermiculite dust (which is common scrap from the exfoliation process), one can produce high temperature adhesives.
The intumescence disappears in the presence of finely divided mineral dust, whereby the waterglass becomes a mere matrix.
Waterglass is inexpensive and abundantly available, which makes its use popular in many refractory applications.

Sodium Silicate
Sets at at 93 C the sodium silicate loses water molecules to form a very powerful sealant that will not re-melt below 815 C.

[nth]

Re: How to insulate a cast iron pizza oven.

What about making a soft "hat" using rockwool covered all sides with heat resistent foil?
Would it stand the high temperatures?
It sure looks easier to make.

[stonecutter]

Re: How to insulate a cast iron pizza oven.

Should work fine, mineral wool has a melting point exceeding 2100*. Just make sure none of it is exposed..it's not food safe.

[nth]

Re: How to insulate a cast iron pizza oven.

I will try mineral wool first.

This evening the kids made me cook pizza, although it was a storm and below zero freezing outside.
The stone in the oven got well over 750*F, but the air inside was not hot enough to crisp the top of the pizza. I guess the crazy weather cooled down the steel way too effective.

(I really think i should have a medal or something... Two times the storm blew the pizza away)