Crumbling Mortar Joints in Sydney CBD

Why we see this constantly in the CBD

Mortar in CBD heritage buildings is almost always lime-based and now over a century old. Years of weather, traffic vibration and previous bad repairs (cement repointing on top of lime mortar) leave joints crumbling and open. Around Pyrmont, Ultimo and the Rocks we routinely find walls where the mortar is so soft you can scrape it out with a key. The fix is full rake-out and repointing with a matched lime mortar — never cement, which destroys the surrounding brick or stone.

Sydney CBD is dominated by 19th-century sandstone commercial buildings, Victorian-era warehouses converted to apartments, and pockets of colonial brickwork around The Rocks. Most heritage buildings here use soft lime mortars and Hawkesbury or Pyrmont sandstone. The mix of foot traffic, tight access, and strict heritage controls means jobs need careful planning.

Signs to watch for on your property

• Mortar crumbling or powdering when you scratch it with a key
• Visible gaps in mortar joints, especially on exposed elevations
• Bricks loose in the wall — moving when pushed
• Water stains or damp patches inside appearing where mortar has failed outside
• Plant growth in joints (moss, weeds, small plants)
• Hard grey cement pointing next to softer original mortar
• Brick faces spalling — surface flaking away

How we fix it properly

1. 1. Inspect and mix-match

   We assess the existing mortar — age, composition, colour, profile — and work out what the original mix was. We take samples, test them if needed, and mix replacement mortar to match. For heritage work this is the most important step.

2. 2. Rake out old mortar by hand

   For heritage brick, we rake out joints by hand with chisels or specialist tools — never with angle grinders, which damage soft brick faces. Depth is usually 15–25mm. Slow work but essential for old buildings.

3. 3. Wet the joints

   Old dry brick sucks water out of fresh mortar too fast, which weakens the bond. We pre-wet joints so the mortar cures properly. Sounds simple but making this step is one of the reasons old repointing jobs fail.

4. 4. Point the joints correctly

   Lime or lime-cement gauged mortar, pushed into the joints firmly, tooled to match the original profile — flush, raked, struck, weathered, or tuck pointed depending on the building. Colour-matched to the existing.

5. 5. Cure slowly

   Lime mortar needs slow, damp curing. We cover the work, mist-spray for several days, and protect from direct sun or heavy rain. Rushed curing is why some repoints fail in 5 years instead of 50.