Refractories are heat resistant materials that are used to line high temperature furnaces and other high temperature processing units. Refractories have to be resistant to thermal stress and other heat-related phenomena, and they have to stand up to physical wear, abrasion and chemical corrosion. The refractories have to be more heat resistantthan metals, and they are required for heating applications that go above 1,000 degrees Fahrenheit (538 degrees C).

Boiler refractory care requires periodic inspection and repair of the refractory surface. One of the most critical parts of a boiler is the rear door, and that is one place where the condition of refractory should be given special attention. The person inspecting it should look for broken pieces and large cracks. A certain amount of hairline cracking is expected and not a problem.