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Refractory mortar differs from regular mortar in that it is designed to resist high temperatures. It is the desired product to use when constructing a firebox inside fireplaces, fire pits, boilers, kilns or bake ovens.

Not to be confused with traditional fireclay mortar, major building codes now require refractory mortar for these types of installations, so when installing or repairing a firebox, it is best that you use a product that meets the code requirements and is easy to use. 

How is refractory mortar different? Refractory mortar is made from high temperature binders and carefully selected aggregates that will not break down under high temperatures.

Heat Stop refractory mortars (Heat Stop 50, Heat Stop II, Heat Stop Premixed, and also Domestic Fireplace Mortar) are considered the industry standard. They are naturally grey in color (except Domestic Fireplace Mortar which is beige in tone), but they can also be colored using many cement coloring agents available.

Refractory mortar comes in convenient 10.5 oz. tubes for small repair jobs, but also can be purchased in a premixed formulation in a tub, or as a dry mix in bags (Heat Stop brand). The dry mix is the most economical version.

NOTE: When using Heat Stop premixed, if it appears dry after stirring, you may add a little water to it. It is recommended that you apply any of the above mentioned mortar products into joints with a 1/16″-1/8″ thickness. 


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– We do NOT clean chimneys, nor install chimney liners.

– We do NOT answer questions about YOUR chimney or wood stove.

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