Vermiculite is one type of hydrous silicate mineral, which is classified as phyllosilicate. It is silver to grey in color and naturally found. When vermiculite is heated, it gets expanded and creates some pockets to prevent heat conduction. This expanded vermiculite is light-weight, odorless, fire resistant and absorbent. For these properties, it has been used as insulating material widely. It works properly up to 1300 degree centigrade. Normally, it is normally found in form of small particles. Vermiculite is mixed with cement and used to insulate pizza oven.
Vermiculite is found in market in different sizes. Sizes of vermiculite differ from large pieces to fine particles. Vermiculate insulation is pebble like concrete, which is gold or light brown in color. Vermiculite is mixed with cement at different ratio and applied on oven dome, hearth and top of the oven roof as insulating material. It works as good and very effective insulator in pizza oven. Even, it helps to add another insulating material on pizza oven.
Vermiculite is used to insulate oven dome outside. When dome gets hot inside, it will be hot outside gradually. If there is no proper insulation outside of dome, it will result in heat loss. To prevent heat loss through dome wall vermiculite insulation is applied. For dome outside, vermiculite is mixed Portland cement and lime as a ratio of 13:1:1. At first, dry ingredients are mixed properly and then water is add in small amount and mixed properly by hand or shovel. It may be solid in touch but stays soft. Then you have to apply that mixer on the dome outside with a layer thickness of one inch.
For under hearth insulation, thick layer of vermiculite insulator is applied. Vermiculite is mixed with Portland cement as a ratio of 5:1. At first, these two dry materials are mixed properly and then it is mixed with water as ratio of 6:1 (dry matter: water). During mixing process, 80% of required water is mixed with dry matter first and then rest of 20% water is added. If water is added at a time, it may make it runny. There is a precaution of mixing vermiculite with Portland cement that don’t use cement mixture for mixing them because it may destroy the insulating property of vermiculite. The thickness of vermiculite mixer will be three to four inch because this thickness is enough to prevent heat loss hearth inside of pizza oven.
This insulator is also used on top of pizza oven. It is used as an extra layer of vermiculite. In dome and hearth of oven, small thickness is applied but here is thick layer of vermiculite. It results more efficient insulation for pizza oven. It may increases the cost of insulation but if your budget is enough, you should do it without any hesitation.
From 1990, vermiculite has been used as insulator for pizza oven. It is an effective insulator than others. But if it is contaminated with impurities like asbestos, it will be problem. Some vermiculite contains asbestos fibers but lower level of contamination is not concern. High amount of asbestos may cause health illness and for that reason vermiculite with high amount of asbestos should be avoided as insulator.
Asbestos cause several health problems. When vermiculite is heated, asbestos will be released and mixed with air. When a person inhales air contaminated asbestos, asbestos will be accumulated in lung tissue. This will cause different problems like lung cancer and mesothelioma. Thus contaminated vermiculite cause health problem. Before purchasing vermiculite, you should check the level of asbestos.
I appreciate your insight of using vermiculite in a pizza oven dome. Could you please clarify the ratio of vermiculite to concrete and the thickness you recommend to be applied on top and sides of firebrick to maintain the heat inside the oven.
Why not use Perlite? No asbestos issue.
can you do vermiculite / perlite on inside and the brick on outside of dome for cosmetic?
Perlite has arsenic fumes when heated. Use vermiculite and wear a mask when using oven.