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Question DetailsAsked on 10/22/2013

repair missing mortor inside of chimney

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Hello, this is Kiel with Angie's List. You'll want to log in at and search for the category Chimney Repair to see our top rated providers in that area. You can also contact our call center at 1-888-944-5478 or send a written request to for more information.

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Thanks so much!

Answered 6 years ago by KielH


When the bonding mortar between liner sections is missing, a separation between liner sections exists. Many masonry flue liners are laid improperly, apparently without regard for what the NFPA 211 Standard or codes call for. These rules are readily available to all chimney masons, but seem to be rarely followed. The standard calls for "the flue liners to be installed ahead of the construction of the chimney as it is carried up, carefully bedded one on the other in a medium duty, non-water soluable calcium aluminate refractory cement mixture, or its equivilant, with close fitting joints left smooth on the inside. Portland cement bonded mixtures shall not be used." NFPA 211 standard 2000 Edt.

When your chimney gets a "chimney-oscopy" , you know the camera that can see where the eye can't, the sweep can easily diagnose missing bonding mortar, liner cracks, dry stacked liner sections, off set placement with lips and ledges, and smeared mortar over joints. All these conditions prohibit the system from meeting the minimum standard for safe vented combustion.

The solution to actually repair this condition, missing mortar joints between flue sections, is to restore that mortar with the Fire safe Flue Joint restoration system or their competitor. A UL Listed ceramic refractory mortar is applied to the joints with a special applicator designed for this restoration. When complete, the joints have a 20 year warranty. Note that not all chimney flues are candidates for this restoration even though they have missing mortar. Check with a qualified chimney sweep in your area that specializes in this repair type.

The area below the flue but above the fireplace damper is called the smoke chamber. This is the transitional area that reduces the space between the FP opening width and the flue width. This area is often left rough with exposed corbelling, or stair-stepped bricks, if built before 1993. These areas are also poorly sealed. The process for sealing the chamber are two. Hand parging or spray parging. Both do the same thing, hand parging requires access for the repair, removal of the damper and bricks are required for tall chambers. Spray is a newer technology that allows application through the damper opening without removal and replacement costs for access.

I hope this answered your question.

David Lamm

The Classic Chimney Sweep


Answered 6 years ago by David Lamm

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