Chimney stacks are a common feature of homes across the UK’s towns and cities. Constantly exposed to the sometimes-harsh UK weather, chimney stacks often require repairs to prevent leaks and structural issues. Chimney repairs range from minor repairs including repointing and repairing cracks to flaunching all the way to removal and rebuild where damage is severe.
With regular inspection, minor repairs can be carried out before more costly repairs are required. In the article that follows, we’ll outline some of the most common chimney problems along with the repairs that are required to fix them.
The sand and cement mortar used to bind bricks is susceptible to erosion over time because of the effects of wind and rain on this relatively low strength material. Cracks in mortar allow water to enter the brickwork where it freezes and therefore expands, causing further damage. Caught early, missing chimney mortar is a relatively inexpensive issue to remediate with repointing of the affected areas. To repoint chimney brickwork, mortar joints should be raked out to a depth of at least 12mm and repointed with a 1:3 cement / sharp sand mix.
Chimney Brick Spalling
Spalling is a term commonly used to describe crumbling of the brickwork surface that occurs when water penetrates the brickwork, expands, and freezes. Brick spalling is often the direct result of missing mortar joints so repointing where required is a great method of prevention for this issue.
Brick spalling weakens the structure of a chimney and can lead to leaning, and even collapse of the stack. Noticing the problem early will reduce the cost of repairs and often, only the affected bricks or brick courses require replacement.
Chimney Flaunching Repairs
Chimney flaunching (sometimes referred to as capping) is a strong sand and cement mix installed above the top brick course to provide protection from weather and in which to bed chimney pots.
Because flaunchings lack flexibility, cracks can often appear in this area of the chimney. Caught early, small cracks can be repaired using epoxy resins at relatively low cost. Left untreated, cracks in chimney flaunchings can develop into large penetrations which increase the possibility of significant water ingress and internal damage. At this point, replacement of the chimney flaunching is generally required.
Flashings should be formed from sheet metal and are most commonly lead. Although the use of a mortar fillet is not un-common, the brittle nature of mortar means that it often cracks when used in this scenario. Avoid carrying out repairs to chimney abutments using mortar fillets and use lead instead for a longer lasting solution.
A common problem with lead chimney flashings is failed fixings and pointing. Correctly installed lead flashings should be chased into a wall to a depth of 25mm, secured with a lead wedge and pointed with lead sealant which is flexible and therefore tolerant to some degree of movement.
Staying on top of these minor repairs will not only ensure that your chimney is free from leaks but also avoids the need for costly repairs later down the line. Chimney stacks left to deteriorate can collapse completely presenting a serious risk to health and safety and causing catastrophic damage to roofs and buildings.