Failed pointing
The mortar between the bricks erodes with rain and frost. Once joints open up, water gets into the stack and the brickwork loosens. Repointing means raking out the old mortar and refilling the joints with new.
Cracked flaunching and loose pots
Flaunching is the mortar bed that holds the chimney pots in place on top of the stack. When it cracks, water gets in and pots can work loose. The repair is to remove the old flaunching and re-bed the pots on fresh mortar.
Leaking flashing
The join between the stack and the roof is sealed with lead flashing. If the lead lifts or splits, or the mortar holding it fails, rain runs down inside the roof. This is one of the most common causes of damp on a chimney breast.
Spalled bricks and leaning stacks
Bricks that have absorbed water can lose their faces in frost, known as spalling. A stack that leans or has badly eroded bricks may need partly or fully rebuilding from the roof line up.
Unused chimneys
A chimney that is no longer used still needs ventilation. Fitting a ventilated cap or cowl keeps rain and birds out while letting air flow, which helps prevent damp inside the flue.
When to get it checked
- Damp or staining on the chimney breast
- Bits of mortar or brick on the roof or ground
- A pot that looks tilted or cracked
- Any visible lean in the stack
