Lime Mortar vs Cement Mortar: What's the Difference?

One of the most common questions I get asked before a repointing job is: "Does it matter what mortar you use?" The short answer is yes — it matters a great deal. Using the wrong mortar on the wrong property is one of the most common causes of long-term brickwork damage I see across Essex and London, and it's almost always the result of a previous contractor cutting corners or simply not knowing the difference. Here's what you need to understand before any repointing work starts on your home. ## What Is Lime Mortar? Lime mortar is the traditional mortar used in brickwork construction before the widespread adoption of Portland cement in the early twentieth century. It's made from lime putty or hydraulic lime mixed with sand and water, and it has been used in British masonry for centuries. The key characteristic of lime mortar is that it's **soft and flexible**. It allows the wall to move slightly — expanding and contracting with temperature changes — without cracking. It also allows moisture to pass through and evaporate out of the wall, which is why it's often described as "breathable." ## What Is Cement Mortar? Cement mortar uses Portland cement as its binding agent. It became the standard choice from the mid-twentieth century onwards because it sets quickly, is widely available, and is cheaper to apply. Cement mortar is **hard and rigid**. It sets to a strength that is often greater than the bricks themselves, which is fine for modern engineering bricks — but a serious problem for older, softer handmade or stock bricks. ## Why Does It Matter Which One You Use? This is where it gets important. If you repoint an older property — anything built before around 1920 — with a hard cement mortar, you're creating a mismatch between the mortar and the bricks. Here's what happens: - **Moisture gets trapped.** Older brickwork was designed to absorb and release moisture through the mortar joints. Cement mortar seals those joints, forcing moisture to find another way out — usually through the face of the brick itself. - **Bricks begin to spall.** When trapped moisture freezes and expands in winter, it causes the face of the brick to crack and flake off. This is called spalling, and once it starts, it's difficult and expensive to reverse. - **The mortar cracks instead of flexing.** Because cement is harder than the surrounding brickwork, any movement in the wall causes the bricks to crack rather than the mortar joints. Mortar joints are designed to be the sacrificial element — they're far cheaper to replace than bricks. I see this damage regularly on Victorian and Edwardian properties across Essex where a previous contractor has repointed with a standard cement mix. The homeowner often doesn't notice the problem for several years, by which point the damage is already done. ## When Should You Use Lime Mortar? As a general rule: - **Pre-1920s brickwork** — always use lime mortar. This includes Victorian, Edwardian, and Georgian properties, as well as any building constructed with handmade or soft stock bricks. - **Listed buildings and conservation areas** — lime mortar is typically a requirement, not a choice. Your local conservation officer will specify the type and mix. - **Matching existing lime mortar** — if the original mortar is lime-based, any repair or repointing work should match it. Mixing lime and cement in the same wall creates uneven movement and moisture behaviour. ## When Is Cement Mortar Acceptable? Cement mortar is appropriate for: - **Post-1950s properties** built with hard engineering bricks or modern facing bricks - **Below-ground or retaining walls** where high strength and water resistance are priorities - **New build work** using modern materials specified for cement mortar Even then, I'd often recommend a mortar with a lower cement content than standard — a mix that's slightly more flexible and forgiving than pure cement. ## How Do I Know Which Mortar Is in My Walls? If you're unsure what mortar your property currently has, there are a few clues: - **Age of the property.** If it was built before 1920, assume lime mortar unless you know otherwise. - **Colour and texture.** Lime mortar tends to be lighter in colour, slightly softer to the touch, and may have a more uneven texture than cement. - **The scratch test.** Carefully scratch the mortar joint with a key or screwdriver. Lime mortar will crumble and powder relatively easily. Cement mortar will be much harder and may not scratch at all. If you're still not sure, send me a few photos and I'll give you my assessment before any work starts. ## Getting the Mix Right Even when lime mortar is the correct choice, the mix matters. The ratio of lime to sand, the type of lime used (natural hydraulic lime vs lime putty), and the sand aggregate all affect the final colour, texture, and performance of the mortar. I mix mortar on site and test samples against the existing joints before committing to the full area. Getting a close match is something I take seriously — a repointing job should be barely noticeable once it's done. ## The Bottom Line Using the wrong mortar doesn't just look wrong — it causes real, lasting damage to your brickwork. If you have an older property and you're considering repointing, make sure whoever you use understands the difference and specifies the correct mortar for your building. If you'd like me to take a look and advise on the right approach for your property, [get in touch](/contact-us) for a free, no-obligation assessment. I cover Essex and London and I'm happy to give you a straight answer before any work is agreed.