Why do I still feel heat outside my oven?

[Ramiro]

Hi, I thought that using refractory materials to build my oven and insulating it with fiber glass I wouldn't feel any heat in the outside walls of my oven, when I touch the outside walls I don't get burned, but it's hot, is that normal?

Thank you!

[christo]

Could it be that there is still some moisture left in your oven and you are feeling the heat from the steam passing through the insulation?

I was surprised how long it took for the insulation in the floor of my oven to stop conducting significant heat due to it being quite wet after the tarp blew off during a rain.

Christo

[CanuckJim]

Ramiro,

Need a bit more info. You say you used refractory materials, fine. Then you mention fiberglass. Is that what you used, or cal sil batt?

Jim

[Ramiro]

Yes, I usted fiberglass for insulation. I'm located in Colmbia, south america and steel oven manufacturers always use fiberglass to insulate heat from their ovens. The company who sold me the fiberglass told me that it could insulate heat up to 500ºC. Thank you !

[CanuckJim]

Ramiro,

I understand that some locations have reduced material selection. To an extent, it's true in Canada, too. Now that we've narrowed it down to fiberglass insulation, how thick is it? Did you then coat the insulation with anything like a vermiculite/cement mix. In short, how did you go about insulating the dome: what other materials, how thick, etc.?

Jim

[Ramiro]

Hi Canuck: When I bought the fiberglass it had a thickness of aprox. 4 inches. After building the dome with firebricks, I coated it with 2cms of cement mix , and instead of pouring water into the cement mix, people here add a liquid that it is made out of sugar cane, I really don't know the name in english. They add it to the cement mix to make it refractory, they do this usually for making chimneys. Then I put the fiberglass over the dome and coated it again with cement mix of aprox. 2cms, finally I painted the oven.

Thanks!

[christo]

Hi Ramrio,

Is there any insulation under the floor of the oven? If so, what type?

Christo

[Ramiro]

Hi Christo:

Under the oven flor there is also fiberglass coated with cement mix.

Ramiro

[wlively]

It sounds to me the problem is two fold.

One, the fiberglass is good insulation for houses because the temp range is 0-50 deg C. It insulates by trapping air and air is the actual insulator. Fiberglass batts are not very dense. This makes it a very poor insulator at extremely high temps. Ceramic blankets are densely woven and the ceramic fiber itself is a big contributor to the insulation.

Two, if you put 2 cm of concrete on top that mashes down the fiberglass removing the air, which is what is providing the insulation. They only work well when "fluffed" or at maximum thickness.


I am afraid if you want to correct the problem, you are going to have to remove the outside concrete shell and reinsulate. You can use perlite or vermiculite concrete mix. You could add this layer on top of your existing shell if you don't want to remove it, but your oven performance will suffer. However, if you are happy enough with that now and only want to reduce the outside surface temp, then that will do.

[Ramiro]

OK, thanks wlively.