What is the required size of mortared joints when installing firebrick?

The correct size for mortared joints when installing firebrick is typically 1/16 inch. This narrow joint size is preferred because it allows for a tighter and more uniform fit between the firebricks, which is essential for maintaining structural integrity and thermal efficiency in high-temperature applications such as fireplaces, furnaces, and kilns.

Using a smaller joint width helps to minimize the amount of mortar used, thus reducing the potential for thermal expansion issues and cracking. A narrower joint also offers better insulation properties since it limits the pathways for heat losses.

In various applications, the specifications may slightly vary, but the 1/16 inch size is generally recognized for its effectiveness in firebrick installations.