Blanket Insulation

I am planning on building an oven in my backyard, hoping to break ground this April 2009 for the pad.

I am a Ceramic Engineer with over 15 years of field experience with refractories (the majority spent with A.P. Green refractories ... prior to the US closing its manufacturing base and A.P. Green closing its doors).

With that said, I believe that this site offers some of the best information and content. I have been reviewing literature and web sites for the past several years and wonder if a thread dedicated towards insulation might be a good idea. And two words should be added to the available literature:

Mineral Wool.

This is available in two basic forms - as loose "wool" shipped in bags and as boards in a variety of thicknesses (1" and 1 1/2" being the most common). The boards typically are sold (in the United States) in 3 ft. lengths and sold by the "board foot". Note: Mineral wool blanket is - or was - made but not readily available and was usually a special-order product.

The insulating properties of mineral wool are far superior to ceramic fiber at the temperatures encountered with wood-fired ovens. Mineral Wool products typically are rated to up to 1800 F depending on manufacturer and product.

Among furnace engineers, talk about insulation was often discussed in terms of 'equivalent inches of firebrick'. Mineral wool board would have well over 18 equiv. inches firebrick around 1000 F as compared to @ 8" for ceramic fiber blanket (uncompressed), making it a superior insulation and resulting in a cooler surface on the outside of a furnace or oven. And more heat being kept inside where we want it.

And mineral wool board should cost less than half the cost of ceramic fiber.

Availability: I would call up any company that supplies refractories (fire brick,castable & plastic refractories, mortars, ...) and ask them if they sell it or could recommend any boiler repair contractor or other supplier that might have some.

I don't work in the refractory field anymore and do not have the literature at hand any more. But this material has been the much more commonly used insulation on industrial furnaces ranging from small heat-treat ovens on up to the largest molten-metal reverboratory furnaces. Ceramic fiber was not used as insulation behind firebrick due to cost and insulative properties. Ceramic fiber was better suited as a substitute to firebrick - as the actual hot-face lining where gas velocity, chemical attack, dusting, and other factors were not an issue. As an insulation, ceramic fiber is not subjected to these factors and can certainly be used there.

Note: I do not promote ceramic fiber exposure to foods as it will gradually develop (in the presence of sufficient temperatures) a form of silica that is harmful to humans (crystobolite). Wood fired ovens would not ordinarily experience these temperatures, especially being used as an insulation layer behind firebrick. Additionally, the fibers are encapsulated between the firebrick and any cladding so they can't go anywhere. Ceramic fiber is a good product but more expensive for my pocket with a great alternative being available.

The designs I have found here are fantastic and I am looking forward to building my own oven (finally). My only planned change will be substituting mineral wool in place of ceramic fiber as the insulation layer based on my furnace experience and background. Vermiculite will then be the next layer (closest to the outside cold face).

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