Repointing with the wrong mortar is the most damaging routine maintenance error on South African heritage buildings. Cement traps moisture in soft historic bricks, causing spalling, salt damage, and structural decay.
Why lime mortar matters
Historic brick and stone is softer and more porous than modern. Walls are designed to breathe — moisture entering the masonry dries out through breathable mortar joints. Cement mortar:
- Doesn't breathe — traps moisture
- Is harder than historic masonry — concentrates stress on bricks rather than soft sacrificial mortar
- Causes spalling at faces (frost-shattering)
- Encourages salt damage
- Looks visually wrong
Lime mortar types
Hydraulic lime (NHL 2, NHL 3.5, NHL 5)
Lime with natural hydraulic properties — sets in damp conditions. Modern South African standard for most historic repointing.
- NHL 2: very soft, internal or sheltered
- NHL 3.5: typical external repointing
- NHL 5: exposed locations, copings, sea-fronts
Lime putty
Pure non-hydraulic lime, slaked and matured. Slowest to set, most breathable. Used for conservation work on the most delicate buildings.
Specification
- Mix ratio (commonly 1:2 to 1:3 lime:aggregate)
- Aggregate type (matching historic sand colour and grading)
- Compatibility tested before scale application
Process
- Carefully rake out existing mortar to 25mm depth minimum (deeper if loose)
- Use hand tools — angle grinders damage adjacent bricks
- Wash joints thoroughly
- Apply lime mortar in layers (don't fill in one go)
- Compact and finish with appropriate tooling
- Cure under damp hessian for 7+ days
Cost
- Lime repointing: R1,600–R2,800 per m² of wall area
- Cement repointing (avoid): R800–R1,400 per m²
Lime costs more upfront but lasts 80–120+ years; bad cement repointing requires removal and redo in 20–40 years.
Provincial Heritage Resources Authority (PHRA) permit
Repointing of heritage-heritage-listed buildings always requires Provincial Heritage Resources Authority (PHRA) permit. Conservation officers will reject cement specifications.
MCFAR works with heritage specialists on lime-mortar repointing programmes.
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Request a QuoteFrequently Asked Questions
Can I match cement pointing on the rest of my house?
Don't — match the original lime mortar regardless of what's elsewhere. Mixed mortars worsen problems.
How can I tell if my old mortar is lime or cement?
Lime mortar crumbles to powder under a screwdriver; cement mortar is hard and chips.