Repointing your brickwork seems straightforward enough, remove old mortar, fill in with new, job done.

But here’s the reality: repointing mistakes can permanently damage irreplaceable Victorian or Georgian bricks, cause expensive damp problems, and leave you worse off than when you started.

The frustrating part? Many of these errors are made by well-meaning DIYers and even professional contractors who should know better.

Whether you’re tackling your London terrace yourself or hiring someone to do brick repointing in London, knowing what can go wrong is half the battle. Let’s walk through the eight most common repointing mistakes and how to avoid them.

1. Using the Wrong Mortar Type or Strength

This is the big one, the mistake that causes the most permanent damage. The golden rule of repointing: mortar should always be softer than the bricks.

When you use modern Portland cement mortar on soft, old bricks (like the yellow London stock bricks in most Victorian terraces), you’re setting up a disaster. The hard cement can’t flex with building movement and won’t let moisture breathe through.

Instead, water is forced out through the brick faces, bringing salts with it that crystallize and make the brick surface flake away like pastry, that’s spalling. Once your brick faces are gone, they’re gone for good.

For any London property built before 1930, lime mortar repointing in London(usually NHL 3.5) is essential. Yes, it costs more than cement. Yes, it takes longer to cure.

But it’s the right material for the job. A mortar analysis can tell you exactly what was used originally, and matching that composition isn’t just historically correct it’s structurally necessary.

2. Not Removing Mortar to Adequate Depth

One of the most common shortcuts is raking out just the loose, crumbly surface mortar, maybe 5-6mm, then skimming over it with fresh mortar. It looks fine initially, but it won’t last.

New mortar needs depth to bond properly: minimum 12-19mm, or about twice the width of the joint. Think of it like a tooth filling, you can’t just cap the surface; you need depth for it to hold.

On the flip side, going too deep (say, 40-50mm) can weaken the wall and risks damaging the bricks themselves. The sweet spot for most brickwork is 15-25mm. Hand tools like a chisel and hammer give you better control than power grinders, which can easily gouge bricks if your hand slips.

3. Poor Joint Preparation and Cleaning

Here’s a stat that should get your attention: a National Masonry Institute survey found that 67% of repointing failures were linked to inadequate cleaning of joints.

After you’ve raked out the old mortar, you’re left with dust, grit, and loose particles lining the joint. New mortar won’t bond to dust, it needs clean brick surfaces. Use a stiff masonry brush (or even compressed air if you have it) to thoroughly clean out every joint.

Then, dampen the joints with a spray bottle, especially in dry or hot weather. This stops the brick from sucking moisture out of your fresh mortar too quickly.

You want damp, not dripping wet. Yes, it’s fussy. Yes, it adds time. But it’s the difference between pointing that lasts 25 years and pointing that fails in five.

4. Mixing Mortar Incorrectly

4.1 Using the Wrong Sand

Sand isn’t just sand. Using ultra-clean sand like silver sand or sharp sand on its own can cause problems the water rises to the surface and all your sand sinks to the bottom because there’s no loam left to help it cohere.

You need a well-graded sand with some fine particles. As heritage bricklayer Marcus Clark puts it, you need enough “loam left on the sand to help it adhere.” This is one reason mortar analysis and test batches matter, getting the sand right is part of matching the original mix.

4.2 Adding Too Much Water

Mortar that’s too wet is a nightmare. It slops onto brick faces, leaves streaks and stains that are a pain to clean off, and doesn’t cure properly. For lime mortar especially, you want it as dry as you can manage while still being workable, what’s called a “lean mix.”

The squeeze test: when you grab a handful and squeeze, it should clump together but not leave mortar all over your palm or drip through your fingers. Think plasticine consistency, not pancake batter.

Wet mortar might seem easier to work with, but you’ll regret it when you’re scrubbing brick faces trying to clean up the mess.

5. Ignoring Weather Conditions

Weather is make-or-break for repointing. The ideal temperature range is 40-90°F (4-32°C), with no rain forecasted for at least 24-48 hours.

Too cold (below 40°F) and the chemical reaction that makes mortar harden slows or stops entirely. Worse, if water in fresh mortar freezes, it expands and creates tiny pockets throughout the joint. The result? Spalling and pitting that shows up within weeks or months.

Too hot (above 90-100°F, especially with wind) and your mortar dries out faster than it can cure, leading to cracks and weak bonds.

Rain within the first day or two can wash away fresh pointing or prevent proper curing. In London’s unpredictable climate, this means watching forecasts closely and being prepared to cover work with tarps or delay if conditions aren’t right.

Spring and fall are your friends, mild temperatures, lower chance of extremes. Yes, it’s inconvenient to wait for good weather. But repointing in January or during a July heatwave is asking for trouble.

6. Improper Application and Tooling

Application technique matters more than you’d think. Overfilling, where mortar bulges out past the brick surface looks messy and actually sheds water poorly.

Underfilling leaves gaps that expose the joint to weather. And smearing mortar onto brick faces while you work creates a cleaning nightmare and an unprofessional finish.

Timing your tooling is crucial. Tool too early (while mortar’s still wet) and it smears everywhere. Tool too late (once it’s rock-hard) and you can’t shape it properly.

The sweet spot is ‘thumb-print hard’, press your thumb into the mortar and it should hold an impression without sticking to your skin.

Use the right tools too: a pointing trowel (narrow, designed for joints) rather than a general bricklaying trowel, and the appropriate jointer for your profile. For most London brickwork, a concave joint (slightly curved inward) is best for weather resistance.

7. Rushing the Curing Process

Curing isn’t just “drying”, it’s the chemical process where mortar gains its strength. This takes time: minimum 24-48 hours of protection, with full curing taking weeks (especially for lime mortar).

The mistake people make is finishing the pointing and walking away. Fresh mortar needs care. In hot or dry weather, mist it a couple times a day to keep it from drying too fast.

In rain, cover it with plastic sheeting. Protect it from direct sun, strong wind, and frost. Burlap or insulated blankets can help retain moisture and moderate temperature.

Rushing this or skipping protection leads to weak, brittle mortar that fails prematurely. Yes, it’s fussy. Yes, it means checking on your work for days after you finish. But mortar that’s cured properly can last 20-30 years. Mortar that’s rushed might fail in five.

8. Taking Shortcuts: The “Quick Fix” Trap

We’ve all been tempted by the quick fix, filling cracks with caulk or grout, spot-patching problem areas, skimming a thin layer of fresh mortar over the old. These might look okay initially, but they’re not made for long-term performance.

Caulk and grout can’t flex with building movement or breathe with masonry, and patch jobs just postpone the inevitable.

Full, proper repointing takes time and that’s the point. Underestimating the skill and attention required is itself a mistake. If you’re dealing with a Victorian or Georgian listed building, large areas, or you’re simply not confident, hire an experienced stone mason in London who specializes in heritage work. Doing it right once beats fixing botched work twice—and saves you money in the long run.

Conclusion

These eight mistakes are surprisingly common, but they’re all avoidable with knowledge, patience, and attention to detail.

Proper repointing protects your investment, preserves your London property’s character, and prevents expensive repairs down the line.

Is it challenging? Absolutely. Repointing demands skill, the right materials, proper conditions, and time. But whether you’re DIYing your Edwardian terrace or hiring a contractor for your Georgian townhouse, knowing what can go wrong means you can avoid it.

Take the time. Use the right materials. Wait for good weather. And if in doubt, consult a professional who understands traditional masonry. Your bricks will thank you for the next century.

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