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Calcium-Silicate Board

Calcium-Silicate board, or CalSil board, not to be confused with Alumina-Silicate board, is the best material for under the oven floor insulation. It has very good insulation properties, and most importantly, it is very rigid and will never sag under the weigh of a refractory pizza oven. It has very low thermal conductivity, meaning that 2″ is typically sufficient under a residential pizza oven and 4″ works well under a commercial pizza oven. The biggest problem with CalSil board is that it is difficult to find, and quite expensive compared with the alternative of using vermiculite or perlite concrete. CalSil board is roughly twice as efficient as vermiculite or perlite concrete, and much faster and easier to install.

Here is a good description of Calcium-Silicate board.

CalSil board, or calcium silicate insulating board, serves as a high-temperature insulation material in various applications, including pizza oven floor insulation. Comprising calcium silicate, this compound delivers superior thermal insulation properties. These boards exhibit lightweight, rigid characteristics, along with low thermal conductivity, effectively minimizing heat transfer. Their resistance to high temperatures renders them suitable for extreme heat environments such as pizza ovens. In pizza oven floor insulation applications, these boards are typically tailored to fit the oven floor’s size and shape. Positioned beneath the cooking floor, they create an insulating layer that prevents excessive heat loss, enhancing the oven’s energy efficiency, and helping keep the cooking floor hot while making multiple pizzas in a row. Additionally, these boards are fire-resistant, providing an extra layer of safety in cases of accidental fires or intense heat exposure. CalSil board can be readily cut or shaped to meet specific design requirements. Overall, calcium silicate insulating board is the best option for pizza oven floor insulation, thanks to its outstanding thermal properties, durability, rigidity, and high-temperature resistance.