Why Old Brickwork Needs Lime, Not Cement

If your house was built before the 1920s, the chances are its bricks were laid in lime mortar. Those bricks are soft, fired at lower temperatures, and slightly porous. They were never designed to be held together by anything as hard as modern cement, and the mortar was always the weaker, more sacrificial part of the wall.

Lime mortar is breathable and slightly flexible. It lets moisture move in and out of the masonry, and it absorbs tiny movements as the building settles. Cement mortar does the opposite: it sets like stone, seals the joints, and traps damp inside the brick. In winter, that trapped water freezes and expands, and the face of the brick starts to flake away. You end up with spalled brickwork and a mortar that has cracked away from the edges anyway.

So the golden rule is straightforward: replace like with like. If the original mortar is soft and sandy, use lime. Match the strength of the mortar to the strength of the brick, not to what feels toughest in the bucket.

Read the Wall Before You Pick Up a Tool

Before buying anything, spend half an hour looking closely. Scrape a joint with a screwdriver. Lime mortar is pale, grainy and crumbles with light pressure. Cement mortar is grey, hard, and often rings when you tap it. Many older walls have been repointed in cement at some point, and that cement may need careful removal before any lime goes back in.

Check the wider picture too. Are there cracked lintels, bulging patches, or heavy efflorescence — that white salty bloom? Repointing is cosmetic work and will not fix a structural or damp problem. If something looks wrong, get it looked at first.

Finally, if your property is listed or sits in a conservation area, pointing usually needs permission. Contact your local planning authority before you start; it is a five-minute phone call that can save an awful lot of trouble.

The Tools and Materials You Actually Need

The good news is that you do not need much, and none of it is expensive.

• Raking out: a plugging chisel and club hammer, or a mortar rake. Avoid angle grinders if you can — they cut fast but chew through brick edges in a heartbeat.
• Safety: dust mask, safety glasses and gloves. Old mortar dust is unpleasant stuff.
• Pointing: a pointing trowel, a pointing iron (or a bent piece of metal), a jointing tool, and an old churn brush for finishing.
• Mixing: a bucket, a mixing board, and a watering can or spray bottle for damping down.
• Materials: natural hydraulic lime (NHL 3.5 is a forgiving choice for beginners) or lime putty, plus a well-graded sharp sand. Your local builders' merchant or a specialist supplier can match the sand to your area's traditional colour.

Mixing Mortar That Behaves Itself

A good starting mix for pointing is roughly one part lime to two and a half or three parts sharp sand by volume. Mix it dry first, then add water slowly until it looks like thick porridge and holds its shape on an upturned trowel.

Do not be tempted to add cement for strength, washing-up liquid for workability, or PVA for stickiness. Each of these changes how the mortar cures and can undo the whole point of using lime. If you are unsure of the colour, make up three small trial patches on a hidden corner and let them dry for a week before committing to the whole wall.

Weather, Timing and Curing

Lime is far more sensitive to the weather than cement, and this is where most beginner jobs go wrong.

• Temperature: work between about 5°C and 25°C. Never point in frost — lime will not set and will crumble out over winter.
• Rain: keep the wall dry for at least 24 hours after pointing. Have tarpaulins or sheeting ready.
• Sun and wind: strong sun or a drying breeze pulls water out too fast, causing cracks and poor adhesion. Overcast, gently damp weather is perfect.
• Curing: lime needs moisture to set properly. Mist the finished work daily for a few days in warm weather.

Spring and early autumn are the sweet spots. Work in small sections — a square metre at a time — so you can finish, tidy and cover before conditions change.

The Pointing Itself, Step by Step

Rake out the old mortar to about 15–20mm deep, or roughly two and a half times the width of the joint, whichever is less. Brush the joints clean of dust, then dampen the wall with a fine spray so the new mortar does not have the moisture sucked straight out of it.

Press the mortar into the joints in small amounts, working it in firmly with the pointing iron rather than smearing it across the brick faces. Build it up in thin lifts until it is slightly proud, then let it firm up for twenty minutes or so. Finish with a churn brush for a traditional brushed texture, or a jointing tool to match the original profile — usually flush or gently recessed. Finally, brush off any smears while the mortar is still green, and leave the wall alone to cure.

One last piece of advice: do a small, hidden section first. Lime rewards patience, and a test patch will tell you more about your mix, your sand and your technique than any guide can.