Why Failed Pointing Causes Damp
Why Failed Pointing Causes Damp
Mortar joints account for a significant proportion of a brick wall's surface area. When these joints deteriorate, water has a direct path into the building fabric. Understanding how pointing fails helps landlords appreciate why timely repointing is one of the most cost-effective maintenance tasks available.
How Mortar Deteriorates
Mortar joints are designed to be sacrificial. They are softer than the bricks they surround and are intended to absorb weathering stress rather than allowing the bricks themselves to deteriorate. Over time, wind-driven rain washes away the surface of the mortar, frost causes micro-cracking as trapped water expands, and chemical reactions with atmospheric pollutants break down the binder. The result is progressively recessed, cracked, and crumbling joints.
How Water Enters Through Failed Joints
Once a joint has recessed by a few millimetres, it creates a ledge that holds water against the wall rather than shedding it. As erosion continues, cracks form that allow water to penetrate deeper into the wall core. In exposed locations or on elevations facing prevailing rain, this process accelerates. The wall gradually becomes saturated from outside inward.
The Path to Internal Damp
Water that enters through failed joints does not always appear directly behind the defective area. Moisture follows gravity and capillary action, tracking along mortar beds, down wall ties, and around lintels. This means internal damp patches may appear some distance from the actual point of entry, making source identification challenging without professional investigation.
Why Painting Over Damp Never Works
Landlords sometimes respond to tenant damp complaints by redecorating internally. This treats the symptom rather than the cause. The source of moisture remains active, and within weeks or months the damp stain reappears. The correct approach is to identify and repair the external defect first, allow the wall to dry, then redecorate.
The Repointing Solution
Professional repointing involves cutting out deteriorated mortar to an adequate depth and replacing it with new mortar matched to the original in composition, colour, and profile. This restores the weathertight integrity of the wall and prevents further water ingress. For older buildings, lime-based mortars are typically specified to maintain breathability.
When to Repoint
Repointing is due when joints are visibly recessed, crumbling, or cracked. On exposed elevations, this may be every 25-40 years. On sheltered faces, joints may last considerably longer. The key indicator is the condition of the joints themselves rather than waiting for internal damp to develop, by which point the wall has been absorbing moisture for an extended period.
Cost-Effective Prevention
Targeted repointing of the worst-affected areas, particularly at high level where exposure is greatest, is far cheaper than dealing with the consequences of prolonged water ingress. Internal replastering, redecoration, timber treatment, and potential structural repairs all cost significantly more than preventive repointing.