Why old chimneys fail – and what you can do about it

chimney stack and pot

Walk through any town or city and you’ll see hundreds, if not thousands, of chimneys. Many of these were built at a time when solid fuel was the only source of heating.

Some are still in use today. Indeed, rarely a day goes by where I don’t sweep one. And rarely does one get swept without showing signs of decay. Eventually, one by one, they will have to be relined if they are to continue to be used. It’s rarely greeted with joy by the owner of the property, but to carry on without having remedial works take place is foolish and can have tragic consequences.

There’s a host of reasons why flues leak and therefore fail. One common reason is mortar failure.

Just like a wall in your house, a chimney is made up of bricks and mortar. Over the years, the mortar turns back into a sandy-like substance and falls away from the bricks, leaving a gap. This can happen through either weathering, or through deposits left in the flue by using it with a combustion appliance. Fumes can escape through these gaps and into another flue. This is a very dangerous scenario as the fumes could then leak into part of your property, or if it is on a shared wall/chimney stack, into a neighbouring property

Gaps in a chimney where the mortar used to be

Gaps in between the brickwork in a flue – here you can see the adjacent flue

Another cause of flue failure is brick fall/midfeather collapse.

It’s important to remember that most flues in a chimney stack are separated by just a single course of bricks. This is called the midfeathers. Over the years, because the mortar which was used to bed the bricks in when the chimney was first built loses its integrity, bricks can start to wobble and become dislodged. In serious cases, the midfeathers can collapse, causing the flue to become blocked. In that scenario, the midfeathers should be rebuilt before you can even start thinking about the best way to start using the flue again.

So how do you know if your old chimney has failed? As a sweep, the most common way is when I do a smoke evacuation check and see smoke emitting from two chimney terminals rather than just one. On a day to day level, you may start smelling smoke or fumes in another part of your home, or a neighbouring property.

Flue pressure tests can be undertaken, but in most circumstances (i.e. – if you are wanting to install a stove or woodburner) it’s more efficient simply to get the flue lined. Pressure tests are also not a guarantee that a flue which passes won’t fail the following day either.

Once flue failure has been identified, then it’s important that the flue is not used until suitable steps have been taken to remedy the situation. Usually, this involves re-lining the chimney. This is something you need expert advice on, as every flue/installation is different.

One final point to make on this is that flue failure is not uncommon. Everything fails eventually and flues are no different. Expecting them to last years and years isn’t realistic. The good news is that there are options available to you. Talk to your local sweep and they should be able to guide you. Further information on this topic is available here.

Mr Soot Chimney Sweep is a HETAS Approved Sweep, and member of the Guild of Master Chimney Sweeps, offering a professional and friendly chimney sweep and stove service in Wigan, Stockport, Southport, Ormskirk, Chorley and surrounding areas. Book Mr Soot online or call 0800 0541154.

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