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Refractory Mortar

Refractory mortar is a specialized adhesive used in the construction and repair of high-temperature environments, particularly for setting firebricks in applications such as kilns, furnaces, fireplaces and pizza ovens. Composed of fine aggregates for workability, and a calcium aluminate cement binder, this mortar is engineered to withstand extreme temperatures and provide a durable bond between firebricks, ensuring the integrity of the overall structure. Its ability to resist thermal stress and expansion makes it an essential component in creating heat-resistant linings for various industrial and residential heating units, and a good, but expensive option for anyone building a brick pizza oven.

Setting firebricks with refractory mortar involves meticulous application to create a strong and reliable bond. The mortar is mixed with water to achieve a workable consistency, and it is then applied between the firebricks during the construction or repair process. The goal is to create tight joints that can withstand the high temperatures generated in the operation of the heating equipment.

Off-the-shelf refractory mortars that air set (they don’t require very high temperatures to sinter) and form a waterproof bond for outdoor use are becoming harder to find in the US, with the serious contraction of US steel and industrial manufacturing, and fireplaces falling out of favor. They have also gone way up in price. HeatStop is a US-producer of refractory mortars, and you can sometimes find their products at masonry supply stores. And sometimes not.

An alternative to true refectory mortar is to make a non-refractory high-temperature mortar using a 3:1:1:1 mixture of fine mesh sand, Portland cement, fireclay and hydrated lime. While Portland cement starts to break down at temperatures as low as 400ºC (732ºF), temperatures that your pizza oven dome will experience every time it is fire, the fireclay and hydrated lime serve as binders, holding the material together over time.