When repointing historic brickwork, why is lime-putty mortar preferred over cement-based mortars?

• A. Because it is softer and more permeable, preventing damage and preserving moisture movement.
• B. Because it is harder and more durable than cement mortars.
• C. Because it provides higher thermal resistance.
• D. Because it requires no curing time.

Answer: (A)

Historic masonry needs a mortar that behaves like the original: soft, breathable, and able to move with the wall. Lime-putty mortar fits that need because it’s softer and more permeable than cement-based mortars. Its porosity lets moisture move through and dry out, reducing the risk of trapped damp, salts, and cracking from moisture变化. The lime mortar also has a bit of elasticity, so it can accommodate small movements of the bricks without binding them rigidly. Cement-based mortars, by contrast, are hard and less forgiving; they don’t breathe as well and can create a rigid joint that traps moisture, stresses bricks, and leads to damage over time. Lime mortars take time to cure through carbonation, which is why “no curing time” isn’t accurate. The emphasis here is on compatibility with historic fabric—softness, breathability, and movement—making lime-putty mortar the best choice for repointing historic brickwork.