A damp proof course (DPC) is a horizontal or vertical barrier built into masonry to stop moisture rising from the ground into walls, floors, or roofs. Rising damp occurs through capillary action: porous materials like brick, mortar, and concrete draw water upward like a sponge. Without a DPC layer, dampness causes plaster to crumble, paint to peel, flooring to loosen, and timber fittings to warp. For on-site teams, understanding where to place DPC and which materials to choose ensures durable, dry structures.
The primary purpose of DPC is to block moisture movement within the structure. Key functions include preventing the breeding of mosquitoes and growth of termites linked to dampness, stopping unpleasant patches from developing on wall surfaces, protecting painted finishes from moisture damage, preventing plaster softening and crumbling, shielding timber doors and windows from warping caused by prolonged dampness, maintaining floor adhesion and preventing loosening of flooring materials, and protecting pipes and fittings from corrosion due to moisture ingress.
Materials for damp proofing fall into flexible and rigid categories. The choice depends on the structural element and the level of moisture control required. Flexible DPC materials include mastic asphalt, which consists of bitumen mixed with fine sand in the hot state to form an impervious mass, typically spread to a depth of 25 mm to 50 mm. Hot-laid bitumen is usually applied in two consecutive layers at a rate of 1.75 kg/m² over a bedding of cement concrete or mortar. Bitumen felts are supplied as 6 mm thick sheets in rolls, with widths matching brick wall dimensions. Metal sheets such as aluminium, lead, or copper are used through the full thickness of walls and coated with asphalt to a minimum thickness of 3 mm. Plastic sheets and membranes offer a lightweight, durable alternative. Rigid materials include impervious brick, stone, slate, cement mortar, or cement concrete painted with bitumen. While strong, rigid materials cannot withstand transverse stresses and may crack under load, so they are less suitable in applications with significant movement or settlement.
DPC is normally placed at plinth level—just above ground level and below the superstructure walls. In cavity wall construction, install DPC in both the outer and inner wall, typically 150 mm to 200 mm above ground level. Other common DPC locations include below ground floors, around basements, at parapet walls, and around window and door openings.
When selecting DPC materials, ensure they are impervious to prevent moisture passage, strong and durable to resist loads without failure, dimensionally stable to prevent shrinkage or expansion, and free from deliquescent salts such as chlorides, nitrates, and sulphates. Alternative DPC methods beyond traditional layers include surface treatment with waterproof coatings, pressure grouting, guniting, integral treatment, and special construction techniques.
