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Property Surveying Blog

Written by Richard Palmer

In London it is hard to walk down any street without noticing the multitude of chimneys towering above the rooftops.

These are often different shapes, heights, sizes and certainly not all in as good condition as could be hoped!

Much of London’s housing stock is made up of houses built between the 1800’s and 1930’s, where at the time the only source of internal heating were fireplaces. Properties of this age often have them in every room, and would have been used heavily during their time in service.

After the introduction of central heating around the 1960’s, chimneys fell into disuse, and so many were removed or blocked up.

When chimney stacks and their associated parts are not being used or at least inspected periodically they can fall into disrepair, and can cause major problems both inside and outside the property.

In this blog post, I will be detailing three of the most common defects to chimney breasts I have seen over the past year during my RICS APC Training.

Leaning and Unstable Chimneys

Walk down any street of Victorian or Georgian properties and you will see at least one chimney stack which is leaning to one side, or appears to have twisted in place.

This is caused by what is known as ‘Sulphate Attack’. This is a chemical reaction between the alkali lime mortar and the acidic sulphur build up within the flue which consists of the soot from the many fires the fireplace has had.

During periods of bad weather, water ingress from faulty pointing or porous brickwork, dampens the sulphur build up and creates crystals where it reacts with the pointing.

This weakens the chimney by forming deposits inside the mortar joints which are weaker than normal mortar and the weight of bricks above the joint causes the chimney stack to slump or rotate in place. This is visible as the stack will be no longer upright and will often lean, sitting out of verticality.

Left unattended this slight lean can become a major failure of the chimney stack itself, as the now deteriorated mortar will continue to weaken over time, until the bricks are no longer held together by anything.

You could even find the chimney stack falling through your roof, or even worse your neighbour’s roof!

The remedy for this problem is costly and can require the rebuild of the chimney stack. This is why it is important to periodically sweep chimneys to remove old residue and to re-point the mortar as and when is necessary to stop water getting in!

Water Ingress

Chimney stacks are the part of the house which tend to be most exposed to the elements.

During heavy rain, it is inevitable that you will get some ingress of water through the chimney pots or open cracks within the brickwork or mortar. This water will run down the inside of the flue and if your chimney breasts are open land in your hearth.

The  water is then easy to mop up before it becomes a problem, or it will evaporate due to adequate ventilation from the airflow around the grate.

However, if your chimney breasts have been blocked up, and there is no adequate ventilation installed this water cannot escape and so chooses the path of least resistance. This is often into the brickwork, itself or the flooring leading to damp issues and potentially ruined decorations!

The quickest and easiest way to remedy this is by installing adequate ventilation on the blocked chimney breast in addition to repointing the chimney stack regularly.

Some people even put a type of capping on their chimney pots to reduce the amount of moisture that can get in in the first place!

Loose chimney pots

Chimney pots come in a vast range of sizes, materials and decorative finishes, however most if not all chimney pots will rest on top of the brick chimney stack in a thin bed of mortar which is known as ‘flaunching’.

As the highest point of a chimney stack is the pots, they are even more exposed to wind, rain and the elements than the other parts of the chimney, and their associated parts deteriorate faster than the other elements of the chimney.

In older properties the flaunching will have deteriorated, and as parts of the mortar crack and fall away so does the grip of the chimney stack on its pots.

Once the pot becomes detached from the mortar flaunching or the flaunching becomes detached from the chimneystack below, the pot becomes very unstable, and in the next period of high wind it could damage property or even injure a person walking by if it was to fall.

The best way to prevent this from happening is to keep up periodic maintenance on the chimney stacks consisting of checking and reapplying mortar pointing, replacing spalled bricks and checking the stability of both the stack and the capping itself.

If you are not using or maintaining your current chimney stack and fireplaces, you may want to consider removing them entirely as where disuse starts, disrepair quickly follows!

Here at Berry Lodge, our Party Wall team regular deals with both chimney breast removal and chimney stack removal.

If you would like some impartial and helpful advice on chimney stack maintenance, or chimney breast removal, give our team of Surveyors a call now and we will be happy to assist you.