The Problem
The homeowner of this 1958 brick ranch in South Park Ridge called us after noticing two brick had shifted visibly outward at the corbeled cap course at the top of the chimney. From the ground, the brick were still in place but had clearly rotated forward - a sign the mortar bed underneath had failed. The rest of the chimney stack, visible from the roofline up, also showed significant mortar recession across all four faces.
The original mortar crown over the flue liner had cracked through in two places and was allowing water directly into the flue. The homeowner had not used the fireplace in several years, but the open crown was allowing water to track down the interior of the liner.
Our Solution
We accessed the chimney from the roof and assessed the corbel course before starting any other work. Both shifted brick were still recoverable - neither had separated fully from the course below. We removed the two loose brick, cleaned all mortar from the bed and header faces, and rebuilt the corbel course with Type N mortar. Each corbel brick was reset at the correct projection and supported with temporary wooden props while the mortar set to full initial bond.
The full chimney stack above the roofline was then repointed. Mortar was ground to 3/4 inch depth on all four faces, blown clean, and filled in two lifts. Type N mortar was matched to the original mid-century gray tone using a sample from the sheltered joint at the base of the chimney stack where it disappears through the roof deck.
The failed crown over the flue was removed completely. The replacement crown was formed with a sloped profile - 5 degrees pitch on all sides - and overhangs the brick face by 1.5 inches on all sides to create a drip edge.
The Result
The two corbel brick are now rebonded and the corbel course is structurally sound. The chimney stack repointing is sealed against water infiltration. The sloped replacement crown sheds rain away from the liner and the brick below it. The homeowner noted that seeing the loose brick move whenever there was wind had been a source of anxiety for an entire season, and they were relieved to have it resolved before another winter.