Rising damp is a common issue in brick-plastered walls where moisture from the ground travels upward through porous materials like bricks, mortar and
Rising damp is a common issue in brick-plastered walls where moisture from the ground travels upward through porous materials like bricks, mortar and concrete plaster. This capillary action leads to unsightly and damaging consequences such as flaking paint, salt deposits, plaster deterioration and in severe cases structural weakening.
Rising damp occurs when water is absorbed from the soil due to a lack of adequate damp-proofing measures. The problem is exacerbated by poor drainage, inadequate ventilation or the absence of a damp-proof course (DPC). To effectively prevent and mitigate rising damp, it is crucial to consider solutions for both new constructions and existing structures.
Six steps to prevent rising damp
1.
Installing a Damp-Proof Course (DPC)
The most effective way to prevent rising damp in a newly built home is to install a DPC. This horizontal barrier, typically made of polyethylene, bitumen felt or chemical additives, is placed at least 150mm above ground level within the mortar joint. The DPC prevents moisture from wicking upward into the walls.
2.
Choosing the Right Foundation and Substrate
In high-risk areas concrete foundations should be waterproofed using additives and sealants to minimise moisture absorption. The ground beneath the foundation should be well-drained with a properly compacted sub-base.
3.
Using Damp-Proof Membranes (DPMs)
In high-risk areas a damp-proof membrane made of high-density polyethylene or liquid-applied waterproofing can be installed beneath concrete floors and wall footings to act as a moisture barrier. It should be seamlessly integrated with the DPC to ensure complete protection.
4.
Applying Waterproof Additives to Plaster and Mortar
Incorporating water-resistant additives into cement-based plasters and mortars reduces porosity and prevents capillary action. Hydrophobic admixtures can be used.
5.
Proper Drainage and Groundwater Management
Effective site drainage is crucial. The area surrounding the structure should be graded to direct water away from the foundation. Additional measures such as French drains help manage groundwater levels effectively.
6.
Ensuring Adequate Ventilation
Good airflow helps evaporate residual moisture that may infiltrate walls. Installing airbricks, vent aids in preventing damp accumulation.
Preventing Rising Damp in Existing Structures
For homes already affected by rising damp, the following remedial measures can be employed:
1.
Chemical Damp-Proofing Injection
If a DPC was never installed or has failed, a chemical damp-proofing injection is a viable retrofit solution. Silane/siloxane-based water-repellent creams or liquids are injected into drilled holes at the base of the wall to form a moisture-resistant barrier.
2.
Removing and Replacing Damaged Plaster
Salt-laden, damp-affected plaster should be removed and replaced with a moisture-resistant plastering system. Using a breathable, salt-resistant plaster ensures that any residual moisture can escape without causing damage.
3.
Installing Physical Barriers
Retrofit DPC solutions such as electro-osmotic damp-proofing systems or mechanical damp-proof membranes can be introduced to existing walls to halt moisture ingress.
4.
Applying Surface Waterproofing Treatments
Hydrophobic coatings or breathable sealants can be applied to external brickwork to repel water while allowing trapped moisture to escape.
5.
Improving Drainage and Groundworks
Enhancing site drainage by installing a French drain or ensuring downspouts and gutters direct water away from walls is essential in mitigating rising damp.
6.
Increasing Ventilation and Dehumidification
Encouraging airflow through proper ventilation strategies, such as airbricks or mechanical ventilation, helps evaporate trapped moisture. In severe cases, dehumidifiers may be required to lower indoor humidity levels.
Understanding How Damp Moves
Damp migrates through plaster due to capillary action, where microscopic pores in cementitious materials draw moisture upward. As water evaporates it leaves behind soluble salts leading to efflorescence—white, powdery deposits that degrade plaster. Continuous moisture presence results in:
• Plaster deterioration: Bubbling, cracking and crumbling occur as moisture weakens the material.
• Mould growth: Damp conditions encourage fungal growth which can pose health risks.
• Structural damage: Long-term exposure to moisture weakens masonry bonds, leading to potential structural failures.
• Thermal inefficiency: Wet walls have reduced insulation properties, leading to increased heating costs.
By implementing proper DPCs, damp-proof membranes, waterproof additives and efficient drainage new buildings can remain moisture-free. For older homes, chemical injections, ventilation improvements and targeted waterproofing solutions can mitigate the problem effectively.
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