This specification outlines the requirements for the supply, application, and finishing of a bitumen damp-proof course (DPC) at the plinth level of all masonry walls, as indicated on the project drawings. The DPC shall act as a waterproof barrier to prevent moisture from rising into the superstructure from the foundation and plinth. All work shall conform to the applicable sections of relevant codes, including but not limited to IS 1346:1976 (Coating of bitumen for damping, waterproofing and protective purposes) and IS 3067:1988 (Code of practice for provision of damp-proof courses in buildings).
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2. Materials
2.1 Bitumen:
The bitumen shall be of a suitable grade as specified in IS 73:2013, commonly paving bitumen of 80/100 grade, unless otherwise specified. It shall be free from impurities, excessive moisture, and any volatile content. The bitumen shall be heated to a uniform and workable consistency, typically between 160°C and 180°C, under careful supervision to prevent charring or degradation.
2.2 Coarse Sand:
The coarse sand shall be clean, hard, durable, and free from clay, silt, organic matter, and other harmful impurities. It shall be well-graded as per IS 383:2016, preferably of Zone II or Zone III. The sand shall pass a 4.75mm sieve.
2.3 Aggregate (Coarse):
The aggregate shall be crushed stone or gravel, clean, and well-graded, conforming to IS 383:2016. The maximum size of aggregate used shall not exceed 10mm.
2.4 Primer:
The primer shall be a cold-applied bitumen emulsion or a solvent-based bituminous solution, as specified by the manufacturer, for improving adhesion to the masonry surface. The primer must be a product of a reputable manufacturer and shall be applied strictly according to their instructions.
3. Preparation of Surface
The top of the plinth level, where the DPC is to be laid, shall be thoroughly cleaned of all loose material, dust, dirt, and debris. The surface must be level, uniform, and free from any projections or depressions. All joints in the masonry below the DPC level shall be properly raked out and filled with cement mortar to create a smooth, continuous surface. The surface shall be dry before the application of the primer.
4. Workmanship and Application
4.1 Priming:
A coat of bituminous primer shall be uniformly applied to the prepared surface using a brush or roller. The primer application rate shall be as per the manufacturer's recommendations. The primed surface must be allowed to dry completely before the application of hot bitumen.
4.2 Application of Bitumen:
A single coat of hot bitumen shall be poured and spread uniformly over the primed surface. The thickness of this layer shall be approximately 20mm. The bitumen shall be applied in one continuous operation to avoid cold joints and ensure a monolithic layer. Special care shall be taken at corners and junctions to ensure continuous coverage.
4.3 Application of Sand and Aggregate:
Immediately after spreading the hot bitumen, while it is still in a semi-liquid state, a layer of hot coarse sand and aggregate mixture in a 1:2 ratio (by volume) shall be evenly and uniformly spread over the entire surface. This layer shall be compacted by a roller or tamper to ensure that the aggregate is properly embedded into the bitumen. The compaction process shall be carefully executed to achieve a dense, impermeable layer.
4.4 Curing and Protection:
The finished DPC layer shall be left undisturbed for a minimum of 24 hours to allow the bitumen to cool and harden completely. During this period, the DPC shall be protected from foot traffic, direct sunlight, rain, or any other elements that could damage the freshly laid course. No further construction or masonry work shall be commenced on the DPC until it has fully set.
5. Thickness and Finish
The final compacted thickness of the bitumen DPC shall be uniform and not less than 20mm. The top surface shall be relatively smooth and free from any irregularities, providing a level base for the subsequent masonry work.
6. Joints and Laps
All joints in the DPC shall be overlapped by a minimum of 150mm to ensure continuity and prevent moisture ingress. Where the DPC meets door frames or other vertical elements, it shall be properly lapped and sealed to prevent any gaps.
7. Measurement
Measurement for payment shall be made on the basis of the net area of the DPC laid, calculated in square meters (m²), as per the dimensions shown in the drawings. No separate measurement shall be made for the preparation of the surface, primers, materials, or labour; these shall be considered incidental to the main item of work.
8. Quality Control and Testing
- The contractor shall provide test certificates for the bitumen, aggregates, and sand from the manufacturer or a certified laboratory, as required by the engineer.
- Random samples of the bitumen used on site may be taken by the engineer for testing to verify compliance with IS 73:2013.
- The thickness of the DPC shall be checked at random locations to ensure it meets the specified 20mm minimum thickness.
- The final finish and proper laying of the DPC shall be subject to the engineer’s approval before any subsequent work can proceed.
9. Safety Precautions
- All work shall be carried out in a safe manner, following all relevant safety codes and practices.
- Workers handling hot bitumen must be provided with appropriate personal protective equipment (PPE), including heat-resistant gloves, safety goggles, and protective clothing.
- Fire extinguishers shall be kept on standby at all times during the heating and application of bitumen.
- Ventilation shall be ensured in confined spaces to prevent the accumulation of hazardous fumes.
- The contractor shall be responsible for all safety measures on site.
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