Repointing Brick and Stone: How to Repair Cracked Mortar Joints

Mortar joints are the unsung heroes of masonry. They bond units together, accommodate slight movement, and — critically — keep water out of the wall structure. When mortar begins to crack, erode, or crumble, the results can range from cosmetic blemishes to serious structural water damage. Repointing (also called tuckpointing) is the process of removing old, failed mortar and replacing it with fresh material. It's a job within reach of most DIY enthusiasts if approached correctly.

How to Identify Failing Mortar Joints

Look out for these warning signs:

  • Visible cracks running along the joint line
  • Recessed or eroded joints where the mortar has worn back from the face of the brick
  • Crumbling or powdery texture when you press the joint
  • Damp patches on internal walls that correspond to external masonry
  • Efflorescence (white salt deposits on the wall face) indicating moisture movement

As a general rule, if a joint has receded more than 10mm from the brick face, it needs repointing.

Choosing the Right Mortar

This is the most important decision in any repointing job. Using a mortar that's too strong for the surrounding masonry is one of the most common and damaging mistakes. Here's why it matters:

  • Older bricks (pre-1920s) are often soft and relatively weak — they were designed to work with lime-based mortars that allow slight movement and breathe
  • If you point them with a modern cement-rich mortar (which is rigid and impermeable), movement stress will crack the brick face rather than the joint — causing far worse damage
  • Lime mortar should be used for older, softer brick and all historic stone buildings
  • Cement:lime:sand (1:1:6 or 1:2:9) is suitable for most modern brickwork
  • Pure Portland cement mortar is rarely appropriate for repointing — it's too strong and rigid

Tools You'll Need

  • Cold chisel or plugging chisel
  • Club hammer
  • Angle grinder with mortar-raking disc (for large areas)
  • Stiff brush for cleaning out dust
  • Pointing trowel or hawk and small trowel
  • Jointing iron or profile tool
  • Safety glasses and dust mask (essential)

Step 1: Remove the Old Mortar

Use a cold chisel and club hammer to carefully rake out the failing mortar to a depth of at least 15–20mm. Work carefully to avoid chipping the edges of the bricks. For large areas, an angle grinder with a mortar-raking disc speeds up the process significantly — but use it with care and always wear eye protection.

Once the mortar is removed, brush out all loose debris and dust with a stiff brush. Dampen the joints lightly with water before applying new mortar — this prevents the dry masonry from drawing moisture too quickly out of the new mix.

Step 2: Mix Your Pointing Mortar

Mix only what you can use in about 30–45 minutes. A consistent mix ratio throughout the job is important for even colour. If you need to match existing mortar closely, experiment with different sand colours before committing to a large batch.

Step 3: Apply the New Mortar

Use a pointing trowel to press mortar firmly into the raked joints. Work in sections, filling the vertical joints (perpends) first and then the horizontal (bed) joints. Press firmly to ensure good adhesion and eliminate voids. Slightly overfill each joint, as the mortar will shrink slightly as it cures.

Step 4: Profile the Joints

Once the mortar has stiffened to the consistency of putty (typically 1–2 hours depending on temperature and humidity), use your jointing tool to finish each joint to the desired profile. The concave (bucket handle) joint is best for weathering. Match the existing joint profile as closely as possible if you're repointing only part of a wall.

Step 5: Curing and Protection

Protect freshly pointed work from direct sun, frost, and heavy rain for at least 48 hours. In cold weather, use hessian sheeting to prevent the mortar freezing before it's cured. Avoid pointing in temperatures below 5°C.

When to Call a Professional

For small areas of garden wall or modern brickwork, repointing is a very achievable DIY task. However, consider calling a professional mason for:

  • Historic or listed buildings where material choices are critical
  • Large areas of an entire house exterior
  • Any walls where structural cracking (diagonal or step-pattern cracks) is present — these indicate movement problems that go beyond simple repointing

Repointing done well is invisible — the goal is for the repair to look like it was never needed. Done badly, with wrong materials or poor technique, it can cause lasting damage. Take your time, choose the right mortar, and the results will speak for themselves.