Over time, weathering can cause the mortar bed in brickwork to decay allowing water to ingress. The surface of the mortar joint will start to fall out leaving an open joint. Water within the mortar joints can freeze in cold conditions causing further damage. The solution to this problem is a process known as wall repointing.
The process involves raking out the mortar joints either by hand chisel (preferable) or by a power grinder if sections of the old mortar is particularly hard to approximately 20 mm or to the point where sound mortar exists in the brick joint. After cleaning down and wetting, the joints are repointed with mortar that has a similar characteristic to the existing mortar. It is important that the mortar is pushed firmly in the joint leaving no voids.