When Does Mortar Fail? Recognising the Signs That Repointing Is Overdue
Mortar does not last forever. Depending on exposure, mix, and the original workmanship, joints can start failing in as little as 25 years.
Every brick wall is only as good as the mortar holding it together. In Kent, where driving rain from the south-west and regular frost cycles put brickwork under constant assault, mortar joints have a finite life. A lime mortar joint on a sheltered south-facing wall might last 80 years or more. The same mortar on an exposed north-west gable in the Medway Towns could start receding within 30.
What Causes Mortar to Fail?
Three main forces break mortar down. Frost action is the biggest problem in southern England; water enters the joint, freezes, expands by roughly 9%, and fractures the mortar from inside. Wind-driven rain saturates joints on exposed elevations, accelerating the freeze-thaw cycle. Chemical attack from pollution, particularly sulphate attack on cement mortars in areas with high groundwater sulphate content, causes the mortar to expand and crack.
The Visible Warning Signs
- Mortar recessed more than 5mm from the brick face.
- Crumbling or sandy mortar that falls away when scraped with a penknife.
- Hairline cracks running through bed joints or perpends.
- White staining (efflorescence) on the wall face, indicating moisture movement through the joints.
- Damp patches on internal walls near external brickwork.
Lime vs Cement: Getting the Mortar Right
Properties built before roughly 1920 were almost always bedded in lime putty mortar, typically a 1:3 mix of non-hydraulic lime to sharp sand. Repointing these with a hard cement mortar (the standard OPC mix many builders default to) is one of the most damaging mistakes you can make. The cement is harder than the bricks themselves; trapped moisture cannot escape through the joints, so it migrates through the brick face instead, causing spalling. We always specify lime mortar for period properties.
For more on how repointing fits with wider property care, see our article on brickwork costs in 2026. Call Herriott Services LTD on 07887 895382 to arrange a free assessment.