We often adopt an out of sight, out of mind approach when it comes to our chimneys, but restoring neglected stacks is money well spent.
A neglected stack can be an accident waiting to happen — the prospect of chunks of heavy masonry dislodged by storms, crashing on to the roof above your bedroom isn’t a risk worth taking. So, if your building survey flags up defects, It is usually advisable to get things sorted sooner rather than later.
Probably the most common issue with chimney stacks is eroded pointing. In itself this may not sound too serious, but if neglected it will hasten the onset of more serious problems such as instability, water penetration and even disintegration. If caught in time, all that may be required to fix this and prevent further deterioration is a spot of localised Repointing.
Before starting work on chimneys, there are a number of important points to consider:
Firstly, we will temporarily seal up your fireplaces to prevent clouds of soot and debris rattling down the flues, creating mess inside.
Chimneys are sometimes used to support TV aerials, these may need to be taken down and later reinstalled.
Visible cracks, blown bricks, Porous Mortar, loose render or eroded masonry are all signs of damage; so too are signs of mould or damp to walls below.
If there’s any danger that a gust of wind could loosen chunks of render or masonry, then this will obviously need to be remedied urgently. This kind of deterioration is often simply down to the effects of ageing. Over the years, extremes of weather can result in mortar joints and masonry eroding, with small cracks allowing water to penetrate and then freeze, further loosening masonry or blowing render.
As if that wasn’t bad enough, this is a war fought on two fronts — inside the flue, dampness from the condensation of gases on the cold surface can also eventually cause expansion, cracking and chemical erosion of the masonry and mortar. Damage to chimney masonry is sometimes caused by poorly fitted TV aerials, too.
Any areas of spalled or defective masonry must be cut out and replaced. If just the upper brick work has come loose due to soft or eroded mortar, then partial taking down and rebuilding may be needed. This may only apply to the top few courses of projecting corbelled Brickwork.
Eroded mortar joints can be raked out and repointed (taking care to match the original style). Any loose, cracked or hollow areas of render can be hacked off and patch repaired.
Internally, installing a flue liner should protect the masonry, prevent leaks and improve thermal insulation. The cost of installing a new flexible stainless steel flue liner and cowl to an existing chimney will be around £539. This task involves removing the existing pot and flaunching, sweeping the flue, inserting a 9m-long liner and then adding a new gas cowl and flaunching.
Leaks Around a Chimney Stack:
Damp patches or mould on walls, ceilings and chimney breasts – usually evident as green or brown staining – are signs of a leak around the chimney stack.
Causes and implications:
Over time, persistent dampness can result in fungal decay developing in adjacent roof timbers, and can also cause ceilings to bow and eventually collapse.
The most likely cause of damp is defective lead or zinc flashings at the junction with the roof, especially to hidden back gutters (the lead flashings at the back of chimneys on the roof slope — the side you can not see). Mortar fillets are sometimes applied as a cheap, short-life alternative to lead, but they are brittle and prone to cracking — they’re always best replaced with new Leadwork .
Sometimes, rain can get around an otherwise perfectly good Lead Flashing because stacks on older homes do not have a damp-proof course (DPC); modern brick stacks have a DPC of around 150mm above roof level. Without a DPC, water can soak into porous stack masonry and leach downwards into the loft or rooms below. Damp penetration may also be due to eroded mortar joints or damaged brick work.
Defective flashings should be replaced with new lead (this should be of a minimum Code 4 thickness). It is false economy to use cheaper, short-life materials, and the trades best qualified to undertake this task are roofers or specialist leadworkers.
To fit a new lead flashing, the roofer or leadworker will cut a groove in the chimney (usually into a mortar joint) approximately 150mm above the level of the roof; on a slope this is normally in a stepped pattern. They will turn the Lead Flashing at least 25mm into the groove and fix it in place with lead wedges and then seal it with new mortar.
It is worth noting that traditionally, at the sides of a stack, slates and plain tiles have strips of L-shaped lead soakers inserted underneath before being covered with the flashing. Soakers are not necessary with interlocking clay and concrete roof tiles.
In some instances, the existing flashing may simply have come loose or is inadequately sealed to the brickwork, in which case it may just need to be refixed and wedged into existing joints and pointed up with fresh mortar. Where damp is due to porous stack walls that lack a DPC, the problem can sometimes be solved by Repointing eroded mortar joints. If all else fails, try fitting new lead flashings that extend higher up and deeper into the Brickwork.