The Problem
The owner of a 1955 ranch in West Skokie noticed an occasional smell of dampness near the fireplace after wet weather. The damper was working and there was no staining inside the firebox. On exterior inspection, the stack showed visible mortar recession across the upper two-thirds, most pronounced on the north and west faces.
This chimney is a double-flue stack, serving a shared firebox that opens into both the living room and the den. Both flues run through the same brick stack. On the roof, we confirmed joint recess averaging 5/8 inch on the north face and 1/2 inch on the west, with open joints near the top course. The crown was structurally intact but visibly porous - it had lost surface density and was absorbing water rather than shedding it.
Our Solution
We ground all stack joints above the roofline to 3/4-inch depth on all four faces, vacuumed out debris, and dampened the brick before packing. The mortar was Type N batched to match the original 1955 joint color - a medium gray with moderate sand aggregate. We tested against a sheltered north-face joint below the roofline where the original color was still legible, and confirmed the match after a 48-hour cure on a small test section.
All joints were packed in two lifts and tooled concave to match the lower unrepaired courses. At the top two courses where joint loss was most severe, we gave particular attention to full back-of-joint contact, where voids pool water most readily.
The porous crown received an elastomeric seal coat in two passes over the full surface, continuing 2 inches down the brick face at all four edges. This seals the crown surface and covers the crown-to-brick transition where hairline separation typically starts. No demolition was needed because the crown body remained structurally sound.
Both flue liners were inspected from the basement cleanout with a flashlight and camera extension. Neither showed active cracking or joint failure in the accessible clay tile sections. Liner condition was documented in writing.
The Result
The dampness smell did not recur through the following wet season. Stack joints are at uniform concave depth across all four faces. The sealed crown shows no surface water absorption at 60 days. The homeowners have written documentation of the double-flue liner condition.
