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Refractory Castable

Refractory castable is a monolithic material widely used in applications, such as pizza ovens, requiring resistance to high temperatures, thermal shock, and abrasion. Comprising aggregates, binders, and additives, these castables form a refractory mass when mixed with water. The aggregates, such as high-alumina or silica, provide structural support, while binders like calcium aluminate cement, fireclay and hydrated lime hold the particles together. Additives are incorporated to enhance specific properties, such as fibers to reduce the chance of cracking and improve thermal shock resistance.

High-end refractory castable typically found in premium pizza ovens has many characteristics in common with a medium duty firebrick, including a high sustained heat tolerance (2,000ºF+), high compression strength and high density (about 130-135 pcf). High quality aggregates are made of materials that can easily withstand high temperatures, and are produced in a number of shapes and sizes to better interlock, making the material more structurally sound than refractory mortar, and more expensive. A high-quality refractory castable can have as many as 5-7 different alumina and silica aggregate sizes and shapes.

Because refractory cartable is typically made for industrial applications, such as kilns and furnaces, which have much higher working temperature ranges than a pizza oven, high temperature cooking, such as 900ºF+ pizza making doesn’t even begin to stress the material. The bigger issue is the thermal shock that results from rapid heat up and cool down cycles, which explain why some high-end ovens and refractory materials designed for pizza oven, contain one, or more fiber additives.

At the very low end, it is possible to cast a pizza oven dome using non-refractory, fireclay mortar. The resulting oven dome will crack and eventually fail, but for light home use, and the experience of casting your own oven, it can be fun.

Mixing true refectory castable at home using calcium aluminate cement is very difficult, and we recommend against trying. It’s basically impossible to find true refractory aggregates in small quantities and to come up with a home recipe, and adding a sand and gravel aggregate of calcium aluminate cement makes a concrete that is difficult to work with.

Last note. Do not confuse refractory cartable with refractory mortar.