The Damp Proof Course (DPC) is a crucial element in building construction, designed to restrict the movement of moisture through walls and floors. By preventing moisture penetration, the DPC safeguards the structure from dampness and related issues that could compromise both aesthetics and structural integrity.
The material used for the DPC should be non-porous to prevent moisture from passing through. This ensures that the barrier remains effective over time, protecting the structure from dampness.
Materials must withstand both dead and live loads without damage. This means that the DPC should be able to bear the weight of the building above it, as well as any additional loads placed upon it during its lifespan.
The DPC materials should maintain their shape and functionality over time, ensuring long-term effectiveness.
DPC materials should not contain salts like sulfates, chlorides, and nitrates, which can attract moisture and compromise the barrier's effectiveness.
Flexible DPC materials include bitumen felts (hessian or glass fiber-based) and plastic sheeting (polythene). These are commonly used for their ease of application and good performance in various conditions.
Semi-rigid DPCs consist of mastic, asphalt, or a combination of materials arranged in layers. These materials provide a balance of flexibility and rigidity necessary for certain types of construction.
Rigid DPCs are made from first-class bricks, stones, slate, and cement concrete. These materials are chosen for their robustness and ability to provide a formidable barrier against moisture.
When selecting DPC materials, it is important to consider the environment where the DPC will be applied. The materials should be suitable for the specific climate conditions to ensure lasting effectiveness.
The building’s construction and usage must be taken into account when choosing DPC materials. Different structures may require different types of DPCs to address their unique moisture control needs.
Materials should be selected based on the location within the building. For example, above-ground applications might use different DPC materials than those used below ground level.
If the wall thickness is ≤ 40 cm, use any of the mentioned materials. Cement concrete (M15 mix) is commonly used, with added waterproofing materials in damp conditions. Apply two coats of hot bitumen over the concrete DPC for added protection.
For larger areas like floors and roofs, flexible materials such as mastic, asphalt, bitumen felts, or plastic sheets are preferred to reduce the number of joints and potential weaknesses.
To accommodate thermal movements, use flexible materials like mastic, asphalt, bitumen felts, or metal. These materials can handle the expansion and contraction caused by temperature changes.
For cavity walls, use flexible materials such as bitumen felt to bridge cavities over doors and windows, ensuring continuity of the damp-proof barrier.
The DPC should cover the full thickness of the walls, excluding rendering. This ensures that all potential moisture paths are blocked.
The mortar bed must be level, even, and free from projections to prevent damage to the DPC materials during and after installation.
When transitioning from horizontal to vertical sections, a cement concrete fillet (75mm radius) should be provided at the junction to maintain a continuous barrier against moisture.
Ensure that each DPC layer is placed correctly to achieve a complete and continuous barrier across all parts of the structure requiring damp protection.
Figures 1-7 explain various conditions and placements of DPC:
A DPC restricts the movement of moisture through walls and floors.
DPC stands for Damp Proof Course.
