How to Repoint Old Brick and Stonework with Lime Mortar

If you own a Victorian, Georgian, or any pre-1920s house, the mortar between your bricks or stones was almost certainly lime-based. Over a hundred-plus years, it wears away — rain, frost, and time erode the joints until they’re recessed, crumbling, or missing entirely. That’s when you need to repoint.

But here’s the thing most people get wrong: they reach for modern cement mortar because it’s what the builders’ merchant stocks and what they’ve seen used on modern houses. On an old building, cement mortar causes serious problems. This guide explains why you must use lime, and then walks you through the full repointing process step by step.

Why You Must Use Lime Mortar on Old Buildings (Not Cement)

This isn’t a preference or a purist position — it’s building science. Old brick and stone buildings were designed to breathe. Moisture gets into the walls (through rain, rising damp, condensation), and it needs to get back out again. Lime mortar is porous — it lets moisture pass through the joints and evaporate.

Cement mortar is hard, rigid, and essentially waterproof. When you repoint an old building with cement, you trap moisture inside the wall. The water has to go somewhere, so it migrates through the bricks or stones instead of through the joints — and that’s where the damage starts.

What Happens When You Use Cement on a Victorian House

• Spalling bricks — moisture trapped behind cement mortar freezes in winter, blowing the face off the bricks. You’ll see the front of bricks crumbling and flaking away. The damage is irreversible.
• Cracking — cement is much harder than old bricks. When the building moves (all buildings move slightly with temperature and moisture changes), the cement doesn’t flex. Instead, the softer bricks crack.
• Damp — moisture that can’t escape through the joints migrates inward, causing damp patches on internal walls, mould, and damage to plaster and decoration.
• Failed pointing — cement mortar bonds poorly to old bricks that were designed for lime. It often cracks away from the joint faces within a few years, letting water in but not letting it out — the worst of both worlds.

If your house was built before about 1920 and has its original mortar (or old lime repointing), always repoint with lime mortar. No exceptions.

Tools and Materials You’ll Need

• Plugging chisel (narrow, 6-10mm) — for raking out old mortar by hand.
• Club hammer (lump hammer) — to use with the chisel.
• Pointing trowel (narrow) — a small trowel for pressing mortar into joints.
• Hawk — to hold the mortar as you work.
• Stiff brush — for cleaning out joints before repointing and brushing off excess after.
• Spray bottle — for dampening joints and keeping the mortar workable.
• Bucket and mixing tools — for mixing the mortar.
• Safety goggles, dust mask, and gloves — lime mortar is caustic and the raking-out process creates dust and flying chips.

Optional but useful:

• SDS+ drill with mortar rake attachment — speeds up raking out dramatically, but use with extreme care to avoid damaging the bricks.
• Pointing gun/mortar bag — for squeezing mortar into joints. Some people prefer these; others find a trowel easier. Try both.

Raking Out the Old Mortar

This is the slow, unglamorous part of the job — and it’s the most important. Poor preparation ruins repointing more than poor technique.

How Deep to Go

Rake out the old mortar to a depth of at least 20-25mm — that’s roughly the width of your thumb. Any shallower and the new mortar won’t have enough depth to form a durable bond. It’ll peel out within a few winters.

On severely eroded joints where the mortar is already 15-20mm recessed, you may not need to rake much deeper — just clear out any loose or crumbling material until you hit solid mortar or the back of the joint.

Best Tools for Raking Out Joints

By hand (recommended for beginners): A plugging chisel and club hammer. Work along the joint, angling the chisel to break out the old mortar without striking the brick faces. It’s slow — expect to cover about 2-3 square metres per day — but you have complete control and minimal risk of brick damage.

Mechanically: An SDS+ drill with a mortar rake or narrow chisel attachment speeds things up considerably. However, one slip and you gouge the brick face, leaving permanent damage. If you go this route, practice on a hidden area first and use a light touch — let the tool do the work.

After raking out: Brush out all loose debris with a stiff brush, then dampen the joints with your spray bottle. The bricks should be damp but not dripping — this prevents them from sucking moisture out of the fresh mortar too quickly.

Mixing Lime Mortar — Getting the Right Ratio

Hydraulic Lime vs Non-Hydraulic Lime

There are two types of lime used in mortar, and the difference matters:

For DIY repointing, use NHL (Natural Hydraulic Lime). It’s sold in bags like cement, mixes the same way, and has a usable working time that’s manageable. NHL 3.5 is the most common grade for repointing — it provides a good balance of strength and flexibility.

The standard mix ratio:

1 part NHL 3.5 : 2.5 parts sharp sand (by volume, not weight)

Use a well-graded sharp sand, ideally with a range of particle sizes. Building sand (soft sand) creates a weaker mortar — you want sharp sand for repointing. Many suppliers sell pre-mixed lime mortar if you want to skip the mixing — it’s more expensive but eliminates the guesswork.

Mixing process:

1. Measure out the sand and lime dry and mix thoroughly.
2. Add water gradually, mixing as you go.
3. Aim for a stiff, dough-like consistency — firmer than you might expect. It should hold its shape when squeezed but not be crumbly.
4. Let the mixed mortar stand for 10-15 minutes (“knocking up”), then remix. This improves workability.

Important: Lime is caustic. Wear gloves and eye protection when mixing and handling. If it contacts your skin, wash it off promptly. Prolonged contact causes lime burns.

The Pointing Technique

Filling the Joints

1. Work in small sections — about 1 square metre at a time. Lime mortar stays workable for an hour or so, but it’s easier to manage in small batches.
2. Fill from the back of the joint forward. Press mortar firmly into the back of the joint with your pointing trowel, compacting it as you go. Don’t just smear mortar across the face — it needs to fill the full depth.
3. Build up in layers if the joint is deep. For joints deeper than about 25mm, apply in two layers — the first to within 10mm of the face, let it firm up for 30-60 minutes, then apply the final layer flush.
4. Slightly overfill the joint — you’ll trim it back during finishing.

Finishing Styles (Flush, Weathered, Bucket Handle)

The finish style should match the original pointing on your building (if any survives) or be appropriate for the period:

• Flush — the most common historic finish. Mortar is pressed flat to the brick face and brushed when firm. Simple, effective, and appropriate for most old buildings.
• Slightly recessed — mortar is set back 2-3mm from the brick face. Common on older stone buildings where the stone faces are slightly irregular. Looks attractive and is easy to achieve.
• Bucket handle (half-round) — a concave finish created by running a rounded tool along the joint. More common on Victorian and later buildings. Creates a neat, defined look.
• Weathered (struck) — the joint is angled to shed water. The top edge is recessed and the bottom edge is flush. Good for exposed walls but harder to achieve neatly.

To finish flush joints: Wait until the mortar is “thumbprint hard” — firm enough to resist light pressure but soft enough to mark with your thumb. Brush across the joint gently with a stiff bristle brush to remove excess and leave a slightly textured surface that matches the surrounding brickwork.

Curing and Protecting Fresh Lime Mortar

Lime mortar is much more sensitive to drying conditions than cement. Get this wrong and your beautiful pointing will crack and crumble within months.

• Keep it damp for at least 3-5 days. Mist the freshly pointed area with a spray bottle 2-3 times per day, especially in warm or windy weather. Lime needs moisture to cure properly.
• Protect from direct sun. In summer, hang damp hessian sacking or old sheets over the freshly pointed area to prevent it drying too fast.
• Protect from heavy rain. While it’s still soft, driving rain will wash the mortar out of the joints. Cover the area with a tarp if heavy rain is forecast, leaving the bottom open for air circulation.
• Don’t point in freezing conditions. Frost kills fresh lime mortar. Avoid repointing if night temperatures are below 5°C — which in practice means the best months in the UK are April to October.

Full curing of NHL lime mortar takes 4-8 weeks, though it reaches functional strength within the first week. The mortar will continue to lighten in colour over the first few months as it carbonates.

How Long It Took Me to Repoint My 1870s House

It’ll vary for person to person and my focus was on the bottom 1/3 which sped things up, but 2 weeks in total to get it all done.

Common Mistakes That Ruin Lime Pointing

1. Not raking out deep enough — 10mm of new mortar over old crumbling mortar just falls out. Go to at least 20-25mm.
2. Smearing mortar over brick faces — wipe off any mortar on the brick surface promptly. Once it sets, it leaves a stain that’s very difficult to remove from porous brick.
3. Letting the mortar dry too quickly — this causes cracking and poor curing. Mist it. Protect it from sun and wind.
4. Pointing in winter — frost destroys uncured lime mortar. If you see white, powdery mortar crumbling after winter, frost damage is the likely cause.
5. Using the wrong sand — building sand makes weak mortar. Use sharp sand with a range of grain sizes.
6. Mixing too wet — sloppy mortar slumps in the joints and stains the bricks. Keep it stiff.
7. Using cement “with a bit of lime” — a common bodge. Even a small amount of cement makes the mortar too hard and too impermeable for old buildings. Use lime only.

My Recommended Lime Mortar Pointing Kit

Here’s what I’d buy for a typical DIY repointing project:

Total starter cost: roughly £55-90 plus the lime and sand for your specific area. Professional repointing costs £40-80 per square metre, so even a small DIY effort pays for the tools many times over.

Repointing with lime mortar is slow, methodical work — but it’s deeply satisfying. There’s something genuinely rewarding about restoring the joints on a building that’s stood for 150 years, knowing you’ve done it properly. Take your time, respect the materials, and your pointing will last decades.