Repairing chimneys

Question 1

How do you know if a chimney stack is safe?

Answer 1

• If it is leaning visibly or leaning by more than 1 mm in 100 mm, it is unsafe.
• You will have to decide whether to repair it or take it down and rebuild the damaged section.
• You may need to consult a structural engineer

Question 2

How does condensation cause the leaning of a chimney stacks occur?

Answer 2

• A leaning stack is often due to expanding mortar (lean tends to be in southerly direction) caused by sulfate attack, resulting from condensation in flue.
• Condensation occurs mainly in the section of the flue above the roof this is the part that gets cold.
• Within the building, moisture in the stack stays warm and does not condense to the same extent.

Question 3

What is the possible remedial action for less severe wear to chimney stack?

Answer 3

• If not too severe, repoint localised failed mortar and replace individual bricks.
• Use sulfate-resistant mortar in any pointing or rebuilding work on chimneys.

Question 4

What is the possible remedial action if the chimney stack is beyond repair?

Answer 4

• If the stack is beyond repair, the stack may have to be rebuilt above roof level.
• There is the opportunity to improve the design, the standard of construction and the weathering details. (correct bricks/mortar, dpc, flashing & liner)