Chimney Lintel Joint

The lintel lintel joint is a location at the top of the firebox where the main chimney structure meets the brick façade front that also constructs the top of the firebox. Many times the bonding of one section of the main chimney masonry to the front wall masonry is with just normal masonry grout or grout with fireclay. Most of the time, the brick masons will not install brick ties because it is a small rise and the brick is supported by steel lintels.

The main chimney typically has its own foundation, and IRC code R1003.8 states that chimneys should not support any loads except their own weight. The front brick surround can be attached to the surrounding wall with brick ties. The chimney may settle at one rate and the rest of the home at another. This differential settlement may cause shear stresses in the bonding between the chimney and front-facing wall. Along with heat from the firebox, this non-refractory mortar heats up and deteriorates.

If this bonding joint deteriorates and forms cracks and gaps then heat can escape between the main chimney and the front wall. Many times timber stud members are installed above this location, and it can become a fire hazard, so we always recommend repairing gapped or deteriorated lintel joints with C199 refractory mortar.

Above the opening of a masonry fireplace there is a lintel, usually a steel angle iron, that carries the weight of the brick over the opening. The lintel joint described above is where that front section of brick meets the main body of the chimney. Steel and masonry expand at different rates when they heat up, and the lintel sits just above the fire, so this area goes through a lot of stress every time the fireplace is used.

• Cracks in the brick or mortar above the fireplace opening
• A gap at the top of the firebox between the fireplace face and the chimney behind it
• Smoke staining on the face of the fireplace above the opening
• Brick above the opening that is sagging or out of line
• A rusted or bowed steel lintel at the top of the opening
• A smoky smell in the wall or room above the fireplace

Rust deserves attention. As steel rusts it expands, and a rusting lintel can push on and crack the masonry around it.

Inspect. We look at the face of the fireplace, the top of the firebox, the damper area, and the smoke chamber above to see how far the gap or cracking goes.

Remove failed mortar. Loose and deteriorated mortar is cleaned out of the joint.

Repair with refractory mortar. As noted above, we repair gapped or deteriorated lintel joints with C199 refractory mortar, which is made to handle the heat at the top of the firebox.

Address the lintel. If the steel lintel is badly rusted or sagging, it may need to be treated or replaced, and the masonry above it reset.

Check the surrounding areas. Gaps here often go together with problems at the fireplace profile seam, the firebox joints, and the smoke chamber, so we check them as part of the repair.

The wall above a fireplace often contains wood framing. If the lintel joint opens up, heat and smoke can escape from the firebox into that wall cavity instead of going up the chimney. That’s why we treat a gapped lintel joint as a safety repair, not a cosmetic one. Proper chimney clearances and a tight firebox work together to keep heat where it belongs.