The 1974 edition of IS 7198 outlines detailed guidelines for applying bitumen mastic as a damp-proofing solution in buildings. It addresses methods to prevent moisture ingress and rising damp in various structural elements such as walls, floors, and foundations, applicable to both subterranean and above-ground constructions. This code is vital for professionals engaged in waterproofing using bitumen mastic across concrete, masonry, and steel frameworks.
Overview
The 1974 edition of IS 7198 outlines detailed guidelines for applying bitumen mastic as a damp-proofing solution in buildings. It addresses methods to prevent moisture ingress and rising damp in various structural elements such as walls, floors, and foundations, applicable to both subterranean and above-ground constructions. This code is vital for professionals engaged in waterproofing using bitumen mastic across concrete, masonry, and steel frameworks.
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Frequently Asked
IS 7198 designates bitumen mastic as an effective damp-proofing material for preventing moisture penetration in walls, floors, and foundations below ground level. It is especially suitable for creating a continuous waterproof membrane to inhibit rising dampness, including structures subjected to hydrostatic pressure, provided that proper dewatering and curing are maintained. Typical applications include basements, foundations, retaining walls, floors at or beneath ground level, and internal tanking of water reservoirs.
As per IS 7198 Clauses 8.1 and 8.2, the bitumen mastic should be applied in one coat of at least 10 mm thickness on above-ground walls and floors. For vertical surfaces and slopes steeper than 30 degrees below ground, three coats totaling a minimum thickness of 20 mm are advised, with the first coat being thin to enhance adhesion. Horizontal and gently sloping surfaces (30 degrees or less) below ground require three coats totaling at least 30 mm. Subsequent coats should be applied promptly to maintain adhesion and avoid contamination.
Before applying bitumen mastic, the surface must be thoroughly cleaned to remove dust, dirt, and debris, and kept dry during application. Concrete surfaces should be smooth and free from irregularities, while masonry walls may require a smooth plaster finish. Dewatering should be sustained until the bitumen mastic hardens and the structure develops enough strength to resist hydrostatic pressure. Additionally, excavation should create a clear space of at least 300 mm outside walls to allow for drying and application.
For internal tanking, maintain a 300 mm clearance around the outside of walls during excavation to keep surfaces dry, ensure an even base slab, construct walls fully before mastic application, and protect horizontal mastic and angle fillets with a 50 mm thick cement-sand screed. For external tanking, provide a minimum 0.6 m working space outside walls, establish a structurally sound base at least 100 mm thick extending 150 mm beyond wall edges for angle fillets, cover horizontal mastic promptly with a 50 mm cement-sand screed, and protect vertical membranes by erecting a brick wall immediately after application.
IS 7198 advises minimizing openings in tanked walls or floors where feasible. When openings are unavoidable, special treatments must be applied to preserve the continuity of the waterproofing membrane. This includes sealing and wrapping around pipes or cables with bitumen mastic or suitable materials to create a tight, waterproof barrier. Proper surface dryness and continued dewatering until hardening are crucial to maintain the integrity of the damp-proofing around these penetrations.
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