Crumbling mortar in masonry chimneys

Older chimneys that are no longer structurally sound are dangerous, particularly in an earthquake. If still being used for an open fire there is the potential fire risk as well. Engaging a chartered professional engineer to assess and advise on options to restrain, strengthen, demolish or rebuild the chimney is recommended.

Causes

Moisture getting into the mortar

Mortar quality is poor – most commonly found in pre-1930s buildings

Listed under: masonry, Roof, chimneys and flues and fireplaces, moisture, mortar

Cause

Moisture getting into the mortar

Repair

  • if a chimney is structurally sound and damage is only to the edges of the mortar, scrape out loose mortar. Re-point with new mortar. Once dry, paint or clear seal bricks to prevent further moisture ingress

  • if removal of the chimney is necessary or preferred, this does not require a building consent. This exemption is limited to any building up to 3 storeys high as long as the removal does not affect the primary structure, any specified system or any fire separation (which includes firewalls protecting other property). Remember to check roof sarking/framing which sometimes is supported on chimney structures. Be aware also that some bracing walls rely on support from chimneys either side

  • any repair work that is necessary after chimney removal – for example, making good the gaps left in a roof – can also be done without a consent

  • the Building Act states that after the repairs are finished, the building must comply with the Building Code to at least the same level as it did before the work started

  • you should only attempt these repairs yourself if you have the skills, knowledge, experience and tools to complete the job properly. Poor quality work on the building exterior can result in leaks and other problems and may affect your house insurance cover

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Cause

Mortar quality is poor – most commonly found in pre-1930s buildings

Repair

  • if mortar is of poor quality the chimney is likely to be structurally unsound and if the fireplace is used for an open fire it poses a fire risk as well. Removal of a structurally unsound chimney does not require a building consent. This exemption is limited to any building up to 3 storeys high as long as the removal does not affect the primary structure, any specified system or any fire separation (which includes firewalls protecting other property).Remember to check roof sarking/framing which sometimes is supported on chimney structures. Be aware also that some bracing walls rely on support from chimneys either side

  • any repair work that is necessary – for example, making good the gaps left in a roof after chimney removal – can also be done without a consent

  • the Building Act states that after the repairs are finished, the building must comply with the Building Code to at least the same level as it did before the work started

  • you should only attempt these repairs yourself if you have the skills, knowledge, experience and tools to complete the job properly. Poor quality work on the building exterior can result in leaks and other problems and may affect your house insurance cover

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