If there is damp on an upstairs chimney breast, the chimney is the first place to look — not the last.
Why chimneys fail first
A stack is exposed on four faces and above the roof line, so it weathers faster than anything else. Flaunching cracks, mortar joints open, and water enters the masonry and travels downwards inside it.
The cement fillet problem
A cement fillet where the roof meets the stack is a shortcut that fails reliably. Cement and masonry expand at different rates, so the fillet cracks within a few winters and then channels water straight into the junction.
- Correct repair: lead soakers, an apron and stepped cover flashing dressed into the mortar joints
- Correct lead code for the position, with bay lengths short enough to allow movement
- Patination oil applied afterwards to prevent staining on the wall below
Re-plastering a damp chimney breast before the stack is repaired will simply postpone the same job.