Insulation for Pizza oven

[Andy Phillips]

Hi, I have a pizza oven made from refractory cement (see

This works OK, but the walls are not thick enough to retain much heat - therefore, having heated the oven with a wood fire and raked it out, it's only possible to cook about two pizzas before it's cooled down. I'd like to be able to cook at least four pizzas and maybe some bread afterwards. I therefore need to thicken the wall to increase the heat capacity - I thought by adding at least one course of bricks around the sides and top of the oven, followed by an inch or so of render. Question is, do I need to use special heat-proof bricks (eg firebricks) and cement, or can I get away with normal house bricks and mortar? I'm concerned that the mortar and render will crack - when in use, the outer wall of the oven gets too hot to touch for more than an instant - I would guess about 100-140C. Any advice appreciated. Andy

[Barry Harmon]

"Andy Phillips" wrote in news: [e-mail]:

Andy,

Did you build the oven or did a professional oven builder/mason build it?

If you had a professional or mason build it, you should ask him. It would seem to me that having an exterior surface that is oven 100C is not a good thing and should be covered by guarantee.

If you built it, then check your instructions to see if you maybe left out something. If you followed the instructions to the letter, get in touch with the people who provided the instructions.

I'd also worry about to the very short cooking time. This indicates to me that you don't have near the thermal mass you should have.

My experience with industrial annealing ovens was that they didn't transfer too much heat to the outer surface and they took a long time to cool down for maintenance, but it's been 40 years, so I might be a little foggy on the fine points.

Barry

[Dick Margulis]

Andy,

First, Barry should have followed your link. It appears you bought a commercial product. However, what we call "the implied warranty of merchantability and fitness for use" in the US may be a legal concept that does not have an exact equivalent in the UK. In any case, this looks to be the product of a home-based microbusiness, so there wouldn't be much point in pursuing a remedy with them.

So, second, let's look at your proposed solution.

What I've seen done to good effect is to design in a gap between the inner shell (which you own) and the outer shell (which you propose to construct) and to fill that gap with vermiculite insulating fill. Vermiculite got a bad rap because the principal source of it in the US was laced with asbestos. For all I know, all sources of it are laced with asbestos. So you will want to be careful handling it (gloves, long sleeves, respirator), and you do want to ensure that the space you are filling is then sealed in an airtight fashion with some sort of inspection plug at the top where you can add more vermiculite if it settles over time.

This insulating layer cuts down significantly on the overall weight of the oven (a possible concern depending on what it's sitting on) as well as on material costs.

The outer layer can be ferrocement, and you can skip the bricks altogether.

Or you can do it your way, of course. I'd suggest firebrick, as it's lighter in weight and therefore easier on your back as you do the work. Of course it may also be harder to come by, in which case I'd suggest chimney brick (solid clay brick, as opposed to the sort with holes in it that is used for walls).

Good luck!

Dick

[Joe Doe]

They suggest you can leave the fire on and cook with it that way. This is actually what is done in all Neapolitan pizza ovens anyway (live fire cooking). That would be the easiest thing to try first.

See the Forno Bravo site for exhaustive discussion on all aspects of wood fired ovens. See for example

go to their forums

[Andy Phillips]

The oven is a pre-fabricated modular design made of refractory cement - it simply slots together. I agree with Barry that it doesn't have enough thermal mass - but I guess this may be unavoidable considering the design, as thicker materials would be too heavy to lift. As Roland says, the manufacturers suggest keeping the fire running while cooking the pizzas - the problem is the small size of the oven, which prevents me from moving the fire away a sufficient distance from the pizza to prevent that latter from burning. My ideal solution would be to build a custom oven on a larger scale, but I just don't have the space. I'd considered Dick's suggestion of making a separate outer wall and filling the gap with vermiculite, for the reasons he gives in his posting - provides insulation between the inner and outer walls and doesn't add too much weight. I had rejected this because I couldn't figure out how to keep it watertight, ie how to cap it - my diy skills are limited. But your post has convinced me to take another look at this option. Cheers Andy

[Barry Harmon]

Dick Margulis wrote in news: [e-mail]:

Dick,

The asbestos vermiculite was primarily mined in Libby, Montana. The book about that disaster laid it all out fairly well. There weere several sources of vermiculite in the US and Canada. The EPA in the US and the Canadian Health Ministry (I think that's the name) forced Libby and all other asbestos vermiculite off the market in the verey early

1990s.

I would be very surprised if any vermiculite on the market today, especially in Europe, had asbestos in it.

On other subjects,

Keeping the water out between uses is simple, get a tarp.

As for insulation, you could get bats of fiberglass and make a box to put over the top of the oven while it's heating. It'll look like hell, but it'll work and will do until something better comes along.

Keeping the oven heating is a good option.

If things get too intense, just slide a sheet of metal under the pizzas and you'll slow down the burning -- although some of us like a slightly charred pizza.

Barry

[Dick Margulis]

I was aware of only the broad outline, involving Libby and W.R. Grace.

I would be, too. But better safe than sorry. I don't know anything about geology, and whether some vermiculite sources are totally asbestos-free or just "low enough" in asbestos is outside my ken.

What temperature does fiberglass melt at (just asking)?

[Dave Bell]

It's pretty good to over 1000C, and really starts to degrade above 2000C.

Dave

[Barry Harmon]

Dick Margulis wrote in news:135jcbdin74t465 @news.supernews.com:

Note change.

Barry

[Craig Schroeder]

Andy, I've good luck with 3M's Nextel fabrics for some work related applications. They are essentially like Thinsulate fibers but made with ceramics. They are very pliable and easily shaped/folded/stacked, etc. Here's some info:

http://t>Hi,

Craig Schroeder craig nospam craigschroeder com

[Andy Phillips]

Craig,

Cool idea - this got me thinking about whether my aim was to insulate the inner core of the oven to minimize heat loss, or to increase the thermal mass also. Most pizza oven rely on the latter strategy and therefore an outer skin of bricks would be the best option. However, I could try an insulating blanket first. I'll try your links and see what I can find - doesn't sound the cheapest option though!

Cheers

Andy

[AJH]

Not in my experience when I was using some roofing insulation on the "cold" side of a steel drum incinerator. It seemed to melt even before the metal reached dull red (about 700C IIRC).

AJH

[AJH]

Sheffield insulation (amongst others) sell cerablanket or kao wool. This can come presoaked in a rigidiser (calcium silicate which is water glass I think) or you can spray it on.

Once this has been set, I used a propane burner, you can gently smear on some fire cement render, it would make the oven look like an ugly poorly iced cake.

AJH

[pamjd]

(see

This works OK, but the walls

Andy, What a cute oven. I amde a adobe oven from the sunset adobe oven plans, but mine is not true to the ploans but close. I use mine quite a bit. It is permenent in the garden outside the house door.

But to your situation. I think I would wall up the stand with playwood and fillit with sand. great theraml mass. Then I would stretch some chicken wire or hardware cloth over the whole thing, except place of the chimmney, and cover the hwole thing with 2-3 inches of concret, mud and straw mixture. Mine has more mud and concrete in it. During hard winters you might get some cracks but they can be filled with concrete eaily to remedy that. Mine definately is not as cute as yours but man does it hold heat and I can do pizzas, then a big beef roast and 10lb of potatos after. Check out the sunset article as a place to start. I can email you a photo of mne if you like. It is nothing fancy simply functional. I am thinking of covering it with broken dishes and pttery next time I have cracks to repair. PaM