Insulating Toaster Oven

[maliohammad]

Hello,
I am trying to make my 40L toaster oven into a pizza oven, so far I have done this:
-Bought refractory bricks
-Made a setup to control the heat of the oven based on K thermocouple.

Now the last part I am struggling with is insulation, most of the insulation materials are disgustingly expensive here, and the cheaper ones don't see safe to use inside my small apartment (I don't want to itch for days)
My oven has a metal body, really thin and the cooking chamber has plenty of holes into the air layer. After that there is the external metal body. The door is glass without any insulation.
I was thinking of wrapping the heating chamber with a few layers of aluminum foil, same for the door, but reading about it online it seems it is not that effective?
Another thing I thought of is perlite, it is cheap and available locally which is great, only problem it is loose and I am not sure if dumbing between the layers would help or not.
People mix it with cement to build ovens, but I have a toaster oven, can I put a layer of perlite cement on the outside of the cooking chamber? Would it stick? Is there another way to help insulate the oven?

Another thing that I thought of is putting some of the refractory bricks around it but is it a good idea?

My main concern is melting the electronics, a lot of the electronics in my setup are sensitive to heat above 150C, and I can't keep them all outside the oven.

Insight on the topic is appreciated.

[MarkJerling]

I have one question: How do you know this is not going to be a fire risk?

[maliohammad]

Common sense maybe?
The toaster oven came with 0 insulation to begin with and even burnt the electric wire inside it once, so what I am doing can't be worse that what they have done already.
Other than that I have it far from flammable stuff and will only run it when I am near it.

[SableSprings]

I would not recommend trying to make the toaster oven into a pizza oven based solely on the fact you mentioned 150C as your concern for the temp sensitive electronics. You would be looking at around 320C-375C (600-700F) for pizza temps on the cooking floor and even higher surface temps building up in the upper oven areas needed to cook the pizza toppings. Heating Fire bricks up to cooking temps takes a significant amount of time with a wood fire, heating bricks up to temp with toaster oven elements, even with better insulation, would be not be realistic or practical in my opinion for making pizzas.

Is wood or charcoal an option for you in an outside location? Maybe a larger, shared oven might be welcomed in your neighborhood. If it is, then creating a clay or refractory material oven with insulation would be an option. Do it yourself propane/natural gas heating is not recommended.

[maliohammad]

I think we have a different goals when we talk about pizza ovens, my end temp goal is 400-500C, I just want good pizza no need for it to be Neapolitan.
As for ovens other than electric, not really. I live in apartment complex and I have no outdoor space so I am limited to the electric oven.
I know electronics melt, that's why I came here asking about insulation suggestions.
Anyway I ended up choosing this mix for the insulation, will do it once the materials arrive:
-White portland
-Perlite
-Clay
with some steel wiring as reinforcement, will see how it goes.

[SableSprings]

I'm sorry, I was thinking °F and wrote °C. You are absolutely correct, my stated temp was way too high. I have edited my post to what I should have posted as the correct target temp range. A good pizza can be baked through a large range of temperatures, but most folks are looking at around 320C-375C (600F-700F). I still am very concerned that insulating your toaster oven to force higher temperatures will damage the electronic controls that were designed for lower temps. I think anything much above 400C is too high to be able to control cooking the pizza top & bottom without burning it up (of course, that's just my personal opinion based on my experiences ).

As long as you know the risks and that it may damage your toaster oven (or apartment), it will be an interesting experiment. Remember that a good ratio for our brick oven insulation dome cover is 10:1 (10 parts perlite to 1 part cement and a handful of clay for every liter volume of material). The clay simply makes the mixture easier to work. Don't forget that you are going to need significant insulation underneath this oven as well. Be aware that running current through an electric wire can generate a fair amount of heat as well...I have had an electric cable get too hot to handle. Good luck and keep posting your results...it will be an interesting "experiment".

[maliohammad]

Thanks for the advices.
As for the insulation, I want it mainly to protect the outside from the heat of the oven (most electronics outside but I want to keep the relay inside). The heat management is done by a diy thermostat so it shouldn't be too bad. I will test many temps and end up using the one that works for me, that's the fun of it.

As for the mixing ratio, I read in many websites 5:1, 6:1 perlite to white portland ratio. Wouldn't 10:1 crumble apart easily? Do you hold it with another layer of cement with less perlite?

As for the wires dw, I will cover them with insulating covers. The current is 10A max, not that much.

[SableSprings]

We use 5:1 underneath the ovens and 10:1 over the dome. The 5:1 has enough compression strength to support a brick or cast oven, so it is always used as the base insulation if ceramic board is not available or is too costly. A base insulation layer (under the cooking floor bricks) should be at least 10-11 cm (4") thick. Yes, the 10:1 mix is crumbly, but that's the ratio that will hold together and provide adequate insulation over the top & sides. We also look at a 10-11 cm thick layer of this 10:1 mix. Because the 10:1 mix is fairly weak structurally, most people apply it slowly in "rings" or use a flexible board as a form to hold it while it cures (up to a week). After it is applied, dried, & cured - people normally cover it with a layer of stucco or homebrew to protect it. By adding that little portion of clay, mixing is a bit easier and it holds together better...not much, but a little better.

This is going to be interesting...please keep posting on your application of insulating concrete, testing, and experimentation. I hope you can achieve your goals with the 10A circuit.

[MarkJerling]

Common sense maybe?
The toaster oven came with 0 insulation to begin with and even burnt the electric wire inside it once, so what I am doing can't be worse that what they have done already.
Other than that I have it far from flammable stuff and will only run it when I am near it.

What you're describing, namely that the wiring inside is already getting too hot, is where I was going with my thinking is that adding a good layer of insulation around the outside, and also refractory bricks, is bound to increase the heat around the wires to the elements. My concern is not so much around flammable stuff around (although that is, of course, a risk) but more so with overheating the toaster oven itself which, presumably, will not have been designed to handle higher heat than what it was designed for.

Good luck!

[maliohammad]

Hey,
Sable springs, I did some calculations and based on 500C internal temp, a 1:5 perlite mix would get to 150c surface temp, with just 2cm on insulation, 4cm will drop it down to 100c. It could be wrong but it is close enough for me to rely on it.
It would be nice to have those layers of insulation you mentioned, but I am limited to the space between the outer shell and the cooking chamber, I need to stay within that limit as the outer shells helps holding the glass door in place. Will see how it goes and update, it will take some time to get everything ready.

MarkJerling, The insulation is around the inner shell (the cooking chamber) so it will help reduce the heat coming to the wires, other than that I bought refractory covers for the wires to help protect them. The toaster itself has a very basic design, a box of steel with 2 simple heating elements, nothing fancy, thankfully heating elements are cheap so I am willing to risk it.

[maliohammad]

Things are going slowly but in a good direction. After I made a 3d model of my oven I realized I had much more space for insulation that I I originally thought I had. 10cm on the right side (near the electronics), 3cm top and bottom, and 4cm to the left.
Rn doing the perlite cement mix, not bad so far and it is decently stuck, not the strongest but it strong enough to not fall on its own.

I bought some ptfe tape too to cover areas that I want to give extra insulation, 90m of 12mm tape, with a thickness of 0.075mm. Will use this to insulate the plastic housing of the relay from the rest of the insulation, will have a dc motor with a fan to cool it too.

Now I am wondering if finishing the the insulation with gypsum is a good idea or not, I see it being used in a lot of diy projects as the main body of a kiln or a heating mantel.

[Connorwal]

It's much better to not take the risk

[maliohammad]

What risk do you mean, using gypsum as a finishing touch or the project itself? If it is the latter then it is a calculated risk I am willing to take.

[MarkJerling]

I'm not sure gypsum plaster will handle the heat well. I have used it around our fireplace and it's cracked badly. I'll need to redo it with refractory plaster.

[maliohammad]

Thanks, will continue with perlite cement then.