Chimney repairs: cracks, damaged terminals and openings

Why does a chimney flue crack?

Heat-cold cycles cause continuous expansion and contraction in the flue material. Over the years the mortar in the joints cracks and internal fissures appear. In old masonry chimneys this is especially common after many winters of heavy use.

The problem is not only structural. Cracks let combustion gases — including carbon monoxide — escape into the home or into the walls, creating a serious health risk. They also encourage damp to seep in and damage the structure of the building.

Types of repair according to the problem

Cracks in the internal flue

If the cracks are superficial and localised, they can be sealed with specialist refractory mortar. For deeper structural cracks or badly deteriorated flues, the usual solution is to insert a stainless steel liner (relining), which creates a new, safer and sealed flue inside the existing one.

A damaged or broken terminal

The terminal (or chimney cap) sits at the very top of the chimney, exposed to rain, frost, wind and sun. It is one of the parts that suffers most wear. A broken terminal lets water in, causing damp inside the flue and the combustion chamber. It can also make it easier for birds or small animals to get in and nest inside.

The repair can be as simple as replacing the part or, if the support is damaged, it calls for masonry work on the roof. Either way, it is not a job to put off.

A damaged chimney opening

The chimney opening — the transition between the firebox and the flue — takes the direct impact of the fire and the soot. Over time the refractory wears away, the joints open up and draught performance drops. An opening in poor condition can also be a point where smoke leaks inside.

How do we know if a chimney has cracks that cannot be seen?

The most dangerous cracks are the ones you cannot see from inside the firebox, in the stretch of flue that runs through walls or false ceilings. The most common warning signs are: a smell of smoke in rooms without a fireplace, damp patches on walls near the flue, or smoke that does not draw properly for no apparent reason.

At El Foc a Terra we use an endoscopic inspection camera to see the real condition of the flue along its whole length. That way there are no surprises: we know exactly what needs repairing before we quote any price.

How much does it cost to repair a chimney?

It depends on the type of work. Sealing a few joints is very different from relining the whole flue. Replacing a terminal is quick; repairing a badly damaged opening can take considerably more work.

At El Foc a Terra we always give a fixed price before starting. No surprises on the final invoice. Before any repair we inspect the flue and explain exactly what we find and what your options are.

Frequently asked questions about chimney repairs

Can the fireplace still be used if it has cracks?

It is not advisable. Cracks in the flue can let carbon monoxide and toxic gases escape into the home, and they are also a fire risk. Until they are repaired, it is better not to light the fire.

What is chimney relining?

Relining means inserting a flexible stainless steel liner inside the existing flue. It creates a new, sealed and safer flue without knocking down any walls. It is the most common solution when the flue is badly deteriorated.

How often should the chimney terminal be checked?

Ideally once a year, at the same time as the annual sweep. The terminal is the most exposed part and the first to deteriorate. If there have been severe storms or hard frosts, it is worth checking it outside the usual inspection too.

How long does chimney relining take?

A standard relining job is usually completed in one working day, depending on the length and accessibility of the flue. Complex cases can take two days.