The short answer
Yes, it can. A television aerial adds weight and catches the wind, and the pull on its brackets works against old mortar, which loosens the brickwork over time. A small aerial on a sound stack is usually fine, but a large one on tired mortar is a common reason for leaning, cracked or shifting chimneys.
How an aerial puts load on a chimney
An aerial looks light, yet it acts as a lever. The mast is fixed to the stack with a lashing bracket, and the aerial itself sits several feet above the top of the brickwork. Every gust that hits the array tries to rock the mast, and the rocking is passed through the bracket into the corner of the chimney. Wind in Hampshire arrives mostly from the south-west, and an exposed stack on a hillside estate takes it head-on. Repeated movement works at the mortar joints around the bracket until they open.
The weight of the aerial is the smaller part of the problem. The bigger issue is that the mortar in many stacks has already gone soft by the time the aerial is considered. Older stacks were built with lime or weak sand and cement mortar, which weathers from the outside in. Rain, frost and flue gases all attack it from different directions. Once the joints are hollow, the bricks are held mainly by their own weight, and an aerial adds a sideways pull they were never designed for.
Signs the aerial is causing trouble
Look at the stack from the garden, using binoculars if you have them, and check each of these.
- Cracks in the brickwork running diagonally from the bracket position.
- Gaps or missing mortar in the joints near the lashings.
- Brickwork at the top of the stack that seems to lean away from the aerial, or a visible bow in the courses.
- Rust staining from the bracket or strapping, which shows that water is getting into the joint.
- Pieces of mortar or small bricks in the gutter or on the ground below.
- A mast that has begun to lean or twist, which suggests the fixings are moving in the masonry.
Inside the house, damp patches on the chimney breast and cold-weather staining on an upper-floor wall can be the delayed result of water entering at a damaged joint. Our page on signs of chimney damage lists the others to watch for.
When it is safe to keep the aerial where it is
A compact aerial on a stack with sound, full joints is generally no problem, and the bracket has done its job for years. The conditions that make it safe are fairly easy to check. The mortar should be firm when scratched with a key, not powdery. The bracket should sit tightly against the brickwork with its strapping taut. The stack itself should stand plumb and show no step cracks. A clean, well-fitted installation on that kind of chimney can stay.
The risk grows with the size of the array. Large aerials, satellite dishes on long poles and several aerials stacked on one mast catch far more wind, so the bracket has to resist greater leverage. A satellite dish fixed to a chimney is a particular concern, because a dish is a sail. If you have one, ask whoever fits it to use a separate wall or pole mount instead.
What to do if the mortar is already weak
Do not climb a ladder and tighten the lashings. That only transfers more load to loose brickwork and puts you at risk. The better answer is to have the stack looked at before more movement occurs. A roofer can repoint the stack, which means raking out the failed mortar and filling the joints with new, and refix the bracket into sound masonry afterwards. Our guide to chimney repointing explains the process and what it involves.
Where the stack is leaning or the brickwork has cracked right through, repointing alone will not do, and part or all of the top may need rebuilding. We say so plainly, and photograph what we find so you can see it. Our page on leaning chimney stacks covers how we judge that decision.
Moving an aerial the safe way
If the stack is sound but you want the load off it, an aerial can be moved to the gable wall, onto a fascia or onto a separate pole bracketed to the roof timbers, with the cable re-run. An aerial engineer or a roofer working with one can do this, and the work is usually quick. If the aerial is no longer needed, because the household uses broadband or satellite, removing it relieves the chimney completely. When we repair a stack with an aerial on it, we agree beforehand with the owner whether it is to be refitted, moved or removed, so the new brickwork is not drilled twice.
One more practical point: any work on the stack needs safe access. Pulling on an aerial from a ladder at the eaves is how people fall. The pre-work scaffold or a cherry picker is used for the roof job and removed afterwards, and our page on scaffolding for chimney repairs explains when it is required.
What it costs
Repairing an aerial-damaged stack falls within the ordinary range of chimney work. Typical UK ranges reported by cost guides put chimney repair at £500 to £2,000, with an average around £750, and repointing a typical stack at £450 to £1,200. The right figure for your stack depends on its height, the amount of failed mortar, the roof pitch and the access. Your fixed quote follows the survey. For the wider picture, see chimney repairs in Basingstoke.
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