How Chimney Repairs and Repointing Protect Your Home

Why Chimneys Need Regular Repair and Repointing

The chimney stack is the most exposed part of most Irish houses. It stands above the roofline, takes the full force of wind and driving rain from every direction and goes through repeated cycles of heating and cooling when the fire is lit. Over time that exposure wears down the mortar, the cement capping and the flashing that seals the chimney to the roof. Chimney repairs and repointing keep the stack weathertight and structurally sound.

This article explains how chimneys deteriorate, the warning signs to look for, what repointing and other chimney repairs involve and why the work should not be left until a leak appears. Whether your chimney is in daily use or has not seen a fire in years, it still needs looking after.

How a Chimney Stack Is Built

A typical chimney stack on an Irish house is built from brick, block or stone, bonded with mortar. At the top, a sloped cement layer called flaunching holds the chimney pots in place and sheds rainwater away from the flues. Where the stack passes through the roof, lead or another flashing material seals the joint between the chimney and the slates or tiles. Many stacks are rendered, and some have a lead or concrete cap over unused flues.

Each of these parts has a job to do, and each one wears out at a different rate. When any one of them fails, water finds its way into the brickwork, the roof space or the room below.

How Chimneys Deteriorate

Mortar Erosion

Mortar is designed to be softer than the bricks it holds together, so it wears first. Rain, wind and frost gradually wash it out of the joints. Once the joints are recessed and crumbling, water soaks into the brickwork, and freezing water expands and breaks down the mortar even faster. In severe cases bricks become loose and the stack can lean.

Cracked Flaunching

The cement flaunching at the top of the stack cracks over time with temperature changes and frost. Water then gets into the top of the brickwork and around the base of the pots. Loose pots are a serious safety risk in high winds.

Failed Flashing

Flashing is the most common source of chimney leaks. Lead can split, lift or slip, and older cement fillets used instead of lead crack and pull away from the stack. Water then runs down the face of the chimney and straight into the roof space.

Damaged Render

Rendered chimneys can crack and blow, with sections of render coming away from the brickwork. Cracks let water in behind the render, where it is held against the bricks and causes damp and frost damage.

Warning Signs of Chimney Problems

Many chimney defects can be spotted from the ground, especially with a pair of binoculars. Look for:

• Gaps or crumbling mortar between bricks
• Bricks that are cracked, flaking or missing
• A stack that leans or looks out of line
• Cracked or missing flaunching around the pots
• Loose, tilting or cracked chimney pots
• Lifted, split or missing lead flashing where the chimney meets the roof
• Plants, moss or heavy staining on the stack

Inside the house, watch for damp patches on the chimney breast, staining on ceilings close to the chimney, water in the fireplace after rain and damp timbers around the stack in the attic. A musty smell from the fireplace can also point to water entering the flue.

What Chimney Repointing Involves

Repointing replaces the worn mortar between the bricks with fresh mortar. Done properly, it restores the weather resistance of the stack and can extend its life by many years. The work normally follows these steps:

1. Safe access is set up, usually with a roof ladder and chimney scaffold or full scaffolding on taller stacks.
2. The old, loose mortar is raked out to a consistent depth without damaging the brick edges.
3. The joints are brushed clean and dampened so the new mortar bonds well.
4. New mortar, matched in strength and colour to the brickwork, is packed firmly into the joints.
5. The joints are finished to a neat profile that sheds water away from the brick faces.

Using the right mortar matters. A mix that is too hard can crack bricks as the stack moves and leave water trapped in the brick faces. Older chimneys built with lime mortar should be repointed with a lime-based mix.

Other Chimney Repairs Carried Out at the Same Time

Once access is in place, it makes sense to deal with every defect on the stack in one visit. Common repairs include:

• Renewing the flaunching and resetting or replacing loose chimney pots
• Replacing damaged bricks and rebuilding unstable stacks from the roofline up
• Fitting new lead flashing, including soakers and a back gutter on wider stacks
• Capping unused flues with ventilated caps to stop rain getting in while allowing air flow
• Fitting cowls or bird guards to flues that are still in use
• Repairing cracked render and applying a breathable masonry treatment

Our chimney repairs page covers the full range of chimney work, from minor repairs to rebuilding.

Why Chimney Work Should Not Be Delayed

A chimney that lets in water causes damage well beyond the stack itself. Water can rot the roof timbers around the chimney, stain ceilings and chimney breasts and damage plaster and decoration inside. Loose bricks or pots can fall onto the roof or the ground below during a storm, which is a danger to people and property.

Chimney leaks are also often mistaken for general roof leaks. If a leak sits close to the chimney, the flashing and the stack itself are the most likely source. Our roof repairs page explains how other leak sources are found and fixed.

When to Book Chimney Work

Chimney repairs depend on reasonably dry, mild weather, because fresh mortar and flaunching need time to set without being washed out by rain or damaged by frost. Late spring through to early autumn is the best period for repointing and rebuilding work. Urgent repairs, such as a loose pot or slipped flashing after a storm, can be made safe at any time of year, with the full repair completed when conditions allow. Having the chimney inspected in late summer gives time to complete any work before the winter storms arrive.

Unused Chimneys Still Need Care

Many Irish homes now have chimneys that are no longer used, after a change to central heating or the installation of a stove in a different position. An unused chimney still stands in the weather and still needs maintenance. Flues should be capped with ventilated caps to stop rain getting in while allowing air to move, which prevents condensation inside the flue. Some homeowners choose to take a redundant stack down below the roofline and slate or tile over it, which removes the maintenance altogether. A roofer can advise on the best option for your house.

Chimneys wear steadily through mortar erosion, cracked flaunching and failed flashing. Regular inspection and timely repointing keep the stack weathertight and safe, and prevent damp from spreading into the roof and the rooms below.

To arrange a chimney inspection or a quote for repointing and repairs, contact Patrick Hannifin Roofing. Call 085 754 7244 or email patrickhannifinroofing@gmail.com.