Lime Mortar Repointing
Expert lime mortar repointing and pointing for listed and period buildings using traditional NHL and breathable hot lime mixes.
Pre-1919 and listed buildings were constructed intentionally to remain porous and breathe, transferring environmental moisture seamlessly out through structural joints. When modern Portland cement is applied, it traps this moisture, locking it within the stonework and systematically blowing the faces off valuable bricks and stone elements over time. Dave Heath provides expert historical raking and breathable repointing using accurate Natural Hydraulic Lime (NHL) and traditional hot lime mixes to safeguard the structural performance and lifespan of old masonry walls.
FAQs
Q1: What is the difference between lime mortar and cement mortar? A: Lime mortar is made from lime putty or NHL (natural hydraulic lime), sand and water. It is soft, breathable and flexible - it behaves much like the materials it holds together. Cement mortar is made from Portland cement, which is hard, rigid and non-porous. For buildings constructed before 1919, lime mortar is almost always the correct material. Cement is cheaper and faster to use, but it causes serious long-term damage to old masonry.
Q2: Why is cement mortar harmful to old stone buildings? A: Old stone, brick and flint was built to breathe - moisture enters the wall and exits through the mortar joints, which are deliberately the softest part. When you repoint with cement, you seal those joints. Moisture has nowhere to go, so it forces its way through the masonry instead, causing the faces to blow, crack and spall. The damage is often not visible for 10-20 years, but by then it is expensive to fix.
Q3: What is repointing and when does it need doing? A: Repointing is the process of raking out old, failed mortar from between masonry joints to a depth of around 25mm, and refilling with fresh lime mortar. It is needed when the existing mortar has eroded, cracked, or fallen out, leaving open joints that allow water to penetrate the wall. If you can push a key more than 10mm into a joint, it is time to repoint.
Q4: How long does lime mortar take to cure? A: Lime mortar cures much more slowly than cement. Initial set takes days rather than hours, and full carbonation - where the lime reacts with CO2 in the air to form calcium carbonate - takes months to years. This is why lime is vulnerable to frost in the early stages. I never repoint with lime when frost is forecast within 3-5 days.
Q5: How do I know if my pointing needs replacing? A: Look for: mortar that is soft, crumbly or powdery; joints that are visibly recessed more than 5mm from the face of the masonry; cracks running through joints; damp patches on internal walls below external pointing; and any areas where pointing has fallen out entirely leaving open gaps.