A cracked, spalled, or crumbling brick in an external wall lets water penetrate the cavity and cause damp, mould, and structural decay. Replacing a single damaged brick is a straightforward DIY job with the right tools and a methodical approach. Before starting, it pays to understand the different types of bricks used in modern and older construction, as your replacement must match the existing wall precisely in size, material, and appearance.
Why Damaged Bricks Need Prompt Attention
A single broken brick creates problems that extend far beyond the visible defect. Water seeps through cracks and missing faces, travels across the wall cavity, and emerges on internal walls as damp patches, salt staining, and black mould. Over time, freeze-thaw cycles make the damage dramatically worse: water inside a crack expands when frozen, forcing the crack wider and flaking off the brick face in a process called spalling. Once the protective outer face is gone, the softer inner body of the brick erodes rapidly, turning a small crack into a major entry point for moisture.
The full tutorial by the original source covers these causes in depth. You can refer to DIY Doctor’s guide to replacing a damaged brick for more detail on why bricks fail and the specific warning signs to look for around your property.
If several bricks show similar cracking patterns in a straight line, the cause may be foundation movement rather than isolated weather damage. In that case consult a structural engineer before attempting repairs. Common types of brick damage include:
- Spalling – the brick face flakes off due to frost action, exposing the soft core beneath
- Cracking – fine or wide cracks that let moisture in and expand with temperature changes
- Staining – lichen, bitumen, or tar deposits that cannot be cleaned off effectively
- Holes from removed pipes – old overflow or soil pipes leave gaps that need filling with a matching brick
- Impact damage – mechanical damage from vehicles, equipment, or accidental knocks
Addressing any of these issues promptly prevents moisture from travelling deeper into the wall fabric and causing expensive internal repairs. A single afternoon spent replacing a damaged brick can save hundreds in damp-proofing costs later on.
Sourcing the Correct Brick and Matching the Mortar
Before you pick up any tools, you need the right replacement brick and a mortar mix that matches the existing wall. Getting this wrong makes the repair stand out and can reduce the value of your property. Brick sizes in the UK changed from imperial to metric in the 1970s. Older imperial bricks measure approximately 215 mm x 102.5 mm x 65 mm, while modern metric bricks are typically 215 mm x 102.5 mm x 50 mm. For properties more than about 15 years old, you will likely need to source bricks from reclamation yards or specialist suppliers rather than a regular builders merchant.
| Brick Source | Best For | Difficulty |
|---|---|---|
| Local builders merchant | Modern properties (under 15 years old) | Easy |
| Reclamation yard | Victorian, Edwardian, and post-war homes | Moderate |
| Specialist brick supplier | Rare or unusual bricks, matching historic colours | Harder |
| Neighbour or nearby building site | Free spares from local work | Variable |
| Turning the existing brick around | Stained bricks only (clean inner face exposed) | Tricky |
Mortar colour is determined primarily by the sand, not the cement. Sharp sand produces a lighter, greyer mix while soft sand gives a warmer buff tone, so you may need to experiment with different sand types and ratios to get a close match. A 5:1 mix of sand to cement is standard for general brickwork, but if the existing mortar is lime-based you should use a 1:5:2 mix of cement, soft sand, and lime to maintain compatibility and breathability. The mortar mix ratios explained on Build-Construct provides a detailed breakdown of how different proportions affect strength, workability, and final colour. If you cannot find the right sand colour, mortar dyes and tints such as those from Bebbington Brick offer a reliable way to adjust the shade accurately.
Tools and Safety Equipment You Will Need
Having all the tools ready before you start prevents frustrating interruptions and helps you work through the steps in one clean session.
- SDS or heavy-duty power drill – at least 800 W for drilling through mortar joints
- Masonry drill bits – 6 mm to 10 mm diameter, depending on drill power
- Bolster chisel – 50 mm to 75 mm wide for general chiselling work
- Cold chisel and plugging chisel – for tight corners and detailed work
- Brick laying trowel and pointing trowel – for applying mortar accurately
- Pointing tool or short length of hose – for finishing the joints neatly
- Bucket and water – for soaking the replacement brick and wetting the cavity
- Hand brush – for sweeping dust and debris from the cavity
Safety gear is non-negotiable. Drilling and chiselling brick sends sharp fragments flying in all directions. Wear safety goggles throughout the entire job, heavy-duty gloves, and old clothing. For work above ground level, use a secure work platform rather than stretching from an ordinary stepladder. Your pointing technique matters greatly for the final appearance, so having the right pointing tool ready from the start saves time and ensures a professional-looking finish.
Removing the Damaged Brick Step by Step
Removing the old brick is the most physically demanding part. The method you choose depends on whether you need the brick intact or can break it up.
Method A – Removing the Brick in One Piece
Use this method if the brick is only stained and you plan to turn it around to expose the clean inner face, or if you want to minimise dust.
- Drill closely spaced holes through the mortar joint around the entire brick. Keep holes about 10 mm apart and stay 5 mm away from adjacent bricks to avoid damaging them.
- Use a hammer and bolster chisel to knock out the loose mortar: sides first, then bottom, then top.
- Switch to a plugging chisel for tight spots where the bolster does not fit.
- Once all mortar is cleared, wiggle the brick gently from side to side and pull forward. Use the bolster as a lever if needed.
- Clean all old mortar off the brick with a hammer and bolster if you plan to re-use it.
Method B – Breaking Up the Brick In Situ
This is the fastest approach for a brick that is already cracked or crumbling and has no value for re-use.
- Drill the mortar joints as above, then drill the brick itself full of holes from one side to the other, keeping them close together to weaken the structure.
- Hold the bolster chisel at a 35 to 40 degree angle on the brick face and hammer in layers, working from one side across the face.
- Sweep debris outward as sections break away and check that none falls into the cavity behind the wall.
- Once all brick fragments are removed, chip away any remaining mortar from inside the hole using the bolster and cold chisel.
- Sweep the cavity clean with a small hand brush.
Never remove more than two bricks from a wall at one time. Removing more can seriously compromise the structural integrity of the surrounding brickwork. If you have several bricks to replace, do two at a time, let the mortar cure for at least a week, then tackle the next pair. The Brick Development Association website offers detailed technical guidance on brick properties and structural masonry that is well worth reviewing before starting larger projects.
Preparing the Cavity and Fitting the New Brick
With the old brick removed and the cavity clean, preparation before laying mortar makes the difference between a repair that lasts for decades and one that fails within a year.
Soak the replacement brick. Immerse it in a bucket of water for at least five minutes before fitting. This prevents the surrounding bricks from sucking moisture out of the fresh mortar too quickly, which would weaken the bond and cause the mortar to cure brittle and crack.
Wet the cavity surfaces. Use a paintbrush dipped in water or a hand sprayer to dampen the faces of the bricks inside the hole. The same principle applies: dry brickwork steals water from the mortar and compromises adhesion.
Lay the mortar bed. Mix your mortar to the correct ratio. For standard cement mortar use 5 parts sand to 1 part cement. For lime-based existing work use 1 part cement, 5 parts soft sand, and 2 parts lime. Apply a generous bed to the base of the hole covering the full width and depth, then mortar the sides as well.
Apply mortar to the brick top and slide the brick into the hole, wiggling it gently side to side to seat it without dislodging the bed below. Use a spirit level across adjacent brick faces to check it sits flush and level. Understanding how dampness enters buildings and what to do about it helps recognise moisture problems early and prevent them from escalating into major repairs.
Pointing and Finishing the Replacement Joints
The final stage seals the repair against water ingress and makes the new brick blend seamlessly with the existing wall.
Load a small amount of mortar onto your pointing trowel and push it firmly into the gaps around the brick. Work from the sides to the top to the bottom, using the pointed end of the trowel to force it deep into each joint. Keep adding mortar until the gap is completely full and you cannot push any more in around the entire perimeter.
Once all gaps are filled, finish the joints to match the existing pointing style. The most common finish for DIY work is bucket handle pointing, which produces a concave profile. Run a pointing tool or a short length of hose along each joint with even pressure to create a smooth, slightly recessed curve. Alternatively, use the back of the trowel for a flush finish or a jointing rake for a recessed square profile if that matches the original wall.
Let the mortar cure slowly. Cover the repair with a plastic sheet in hot or windy weather and mist it with water once or twice daily for the first three days. This slow curing gives the mortar its full strength and prevents shrinkage cracks from forming around the edges of the new brick. With the pointing complete and the mortar fully cured, the new brick should be barely distinguishable from its neighbours. The repair is weathertight, the wall is structurally sound, and the risk of damp ingress through that location is eliminated for years to come.