Home Projects Tips & Techniques How to Inspect & Repair a Firebox

How to Inspect & Repair a Firebox


A masonry fireplace is a treasured feature in many homes. Most fireplaces are constructed with several different materials, including two or more types of brick and mortar, concrete, concrete block, metal, and fireclay. Routine maintenance is essential to the efficiency and longevity of your fireplace, as well as to the safety of your home.

masonry fireplace

Masonry fireplaces are built according to strict specifications designed to maximize heating efficiency,smoke exhaustion, and above all, safety.
The internal chamber where the fire burns, known as the firebox, is made with heat-resistant firebrick and a special mortar that can withstand extremely high temperatures. For added heat resistance, mortar joints in firebrick construction are smaller than with other types of brick, usually 1/16″ to 1/4″ thick.

The firebox reflects the fire’s heat into the room, and it insulates the surrounding structure from the high temperatures that can cause damage. Therefore, in addition to having your fireplace and chimney inspected and cleaned regularly, it’s a good idea to check the firebox for crumb ling mortar joints and loose, cracked, or chipped bricks.

Signs of severe damage or wear in the firebox may indicate serious problems elsewhere in the fireplace or chimney and should be reported to a professional.
But you can fix most minor problems yourself, provided you use only materials rated for fireplaces. Some refractory mortars are sold premixed so it is not necessary to add water. Whichever product you select, make sure it is rated for use with fire brick.

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How to Inspect & Repair a Firebox

inspectionStep 1 Begin your inspection by cleaning the fireplace thoroughly. If the bricks and mortar joints are not clearly visible, use a fireplace cleaner and a stiff-bristle brush to remove the soot and creosote buildup. Use a shop light and mirror to view the upper areas of the firebox and the damper opening.[divide color=”#808080″]

inspect the bricksStep 2 Using a flashlight, inspect the bricks and mortar in the firebox. Check for loose mortar by lightly scraping the joints with a screwdriver. Look for cracks and feel around for any loose bricks.[divide color=”#808080″]

loose or damaged bricksStep 3 Remove any loose or damaged bricks, and scrape off the old mortar, using a masonry or stone chisel. Clean the edges of the surrounding brick with a stiff-bristle brush. If you need replacement bricks, bring an original one to a fireplace or brick supplier to be sure you get a perfect match.[divide color=”#808080″]

mortar jointsStep 4 Apply refractory mortar to the new bricks, following the mortar manufacturer’s directions. Gently slide the bricks into place until they are flush with the surrounding bricks. Scrape off excess mortar with a trowel. Use a jointing tool to tool the mortar joints.

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