How to repair cracked brickwork

Video by Skill Builder. This walk-through draws on the video “Easily Repair Masonry Cracks | BrickFix Crack Stitching Kit” from the Skill Builder channel, presented by Roger Bisby. Skill Builder covers masonry repair in detail — the section on cutting slots and inserting stainless steel ties is particularly useful for anyone dealing with cracks that keep reappearing.

1. Assess the crack before doing anything else

This is the step most people skip, and it’s the most important one. Before you fill anything, work out whether the crack is active or dormant. An active crack is still moving — caused by ongoing settlement, subsidence, or seasonal thermal movement. A dormant crack happened once and hasn’t moved since.

The simplest test: cover the crack with a small patch of plaster or decorator’s filler, mark the date on it, and check back in six weeks. If the filler cracks or pulls away, the crack is still moving and you need to understand why before you repair it. Stair-step cracks running along mortar joints at 45 degrees, or cracks wider than 5 mm, are worth getting a structural engineer to look at. To be fair, the vast majority of cracks in garden walls and older Kent cottages are just dormant settlement cracks and need nothing more than a tuck and a repoint.

2. Gather your tools and materials

For small mortar joint cracks, you need an angle grinder or cold chisel and club hammer to rake out the joint, a pointing trowel, and a bag of ready-mixed mortar or lime mortar. Match the mortar type to what’s already there — using a hard cement mortar on an old lime-pointed wall will cause more cracking as the rigid mortar can’t flex with the softer bricks.

For cracks that run through the bricks themselves, or long horizontal cracks above a lintel or door opening, crack stitching is the proper repair. You’ll need an angle grinder with a diamond disc, stainless steel helical bar or crack stitching ties, specialist repair mortar (usually a resin or cementitious grout), and a pointing gun or trowel to fill the slot. It sounds involved, but the actual work isn’t complicated once you understand the principle.

3. Rake out and prepare the cracked joint or brick

For a mortar joint crack, use a plugging chisel or angle grinder to rake out the old mortar to a depth of at least 15 to 20 mm. Don’t just scratch the surface — the new mortar needs depth to grip. Brush out all the loose dust with a stiff brush, then dampen the joint with water. Dry brickwork sucks moisture out of fresh mortar too fast and leaves it crumbly.

For a crack stitching repair, use an angle grinder with a 4-inch diamond disc to cut a horizontal slot along the mortar bed joints above and below the crack, or directly over the crack if it runs through the bricks. The slot needs to be wide enough and deep enough to accept your stainless helical bar — typically about 25 mm wide and 30 mm deep. Cut in stages and clear the slot thoroughly. Wear a dust mask and goggles; the dust from old masonry is fine and there’s a lot of it.

4. Apply the repair mortar or filler

For repointing a crack, mix your mortar to a firm, slightly dry consistency. Too wet and it slumps and stains the face of the brickwork. Point the joint from the back out, pushing the mortar in firmly with the trowel and tamping it down as you go. Work in sections of about a metre at a time rather than trying to fill the whole crack in one go.

For a stitching repair, squeeze or trowel your repair grout into the cut slot, insert the stainless bar centrally, and pack grout around and over it until the slot is flush. The bar pins the masonry either side of the crack together and distributes any load, stopping the crack from reopening. Most crack stitching mortars set quickly, so mix small batches and work through them before they go off. Mind you, slow down if the weather is warm — it sets faster than you expect on a sunny day.

5. Finish the mortar joint to match the surrounding pointing

Once the repair mortar or grout is thumbprint-firm — that is, it holds its shape when you press it but doesn’t stick to your thumb — tool the joint to match the existing pointing style. Most older Kent brickwork uses a slightly recessed bucket-handle or flush joint. Run a jointing iron or the handle of a pointing trowel along the joint in one smooth pass. Do it too early and the mortar smears; too late and it’s too hard to tool cleanly.

Brush off any mortar smears from the brick faces with a damp brush before the mortar goes fully hard. Once it’s cured (leave it at least 24 hours, longer in cold weather), check that the colour is a reasonable match. Fresh mortar always looks pale and bright at first — it dulls down as it cures, usually within a few weeks of weathering. If the colour difference is still jarring after a month, a diluted mortar stain can help blend it in.

6. Protect the repair and monitor for recurrence

On exposed sections of wall — a garden boundary wall, a chimney stack, or an extension parapet — consider applying a clear masonry water repellent once the repair has fully cured. These are breathable products that let moisture vapour out while stopping rainwater getting in. East Kent gets a reasonable amount of driving rain off the Channel, and saturated masonry cracks again in a frost.

Keep an eye on the repaired area for the first year. If the crack reopens along the same line, it’s telling you there’s still movement somewhere. Repairing it again without finding the cause is just papering over it. In older properties, a cracked lintel, a failing wall tie in a cavity wall, or tree roots near a garden wall foundation are all worth checking. Most of the time, though, a well-executed repair will hold for many years without any further attention.

When to call a handyman

Call Richard if the crack is wide, runs through multiple bricks rather than just the mortar joints, or keeps coming back after previous repairs. Crack stitching isn’t difficult but it does require an angle grinder and a bit of confidence with masonry tools. It’s also worth getting someone in if the cracking is on a chimney stack, a boundary wall that could fall onto a neighbour’s property, or if you’re unsure whether the crack is structural. Catching these things early costs far less than leaving them.