Bitumen damp-proof course.

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(1) bitumen dpc with hessian base
(2) bituman dpc with fibre base

(3) bituman dpc with hessian base and lead
(4) bitumen dpc with fibre base and lead.

Bitumen dpcs are reasonably flexible and can withstand distortion due to moderate settlement in walls without damage. They may extrude under heavy loads without affecting their efficiency as a barrier to moisture. Bitumen dpcs, which are made in rolls to suit the thickness of walls, are bedded on a level bed of mortar and lapped at least 100 mm or the width of the dpc at running joints and intersections.

Bitumen is much used for dpcs because it is at once economical, flexible, reasonably durable and convenient to lay. There is little to choose between hessian or fibre as a base for a bitumen dpc above ground. The fibre base is cheaper but less tough than hessian.

The lead cored dpc, with a lead strip weighing not less than 1.20 kg/m^2, joined with soldered joints, is more expensive and more effective than the bitumen alone types. It is generally used as the horizontal dpc for houses.

The combination of a mortar bed, bitumen dpc and the mortar bed over the dpc for brickwork makes a comparatively deep mortar joint that may look unsightly.

Bitumen sheet.

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Sheets of bitumen with hessian, fibre or mineral fibre base are spread on the concrete oversite or on a blinding of stiff concrete below the concrete, in a single layer with the joints between adjacent sheets lapped 75 mm.

The joints are then sealed with a gas torch which melts the bitumen in the overlap of the sheets sufficient to bond them together. Alternatively the lap is made with hot bitumen spread between the overlap of the sheets which are then pressed together to make a damp-proof joint. The bonded sheets may be carried across adjacent walls as a dpc, or up against the walls and then across as dpc where the membrane and dpc are at different levels.

The polythene or polyester film and self-adhesive rubber/bitumen compound sheets,under ‘Tanking’, can also be used as damp-proof membranes, with the purpose cut, shaped cloaks and gussets for upstand edges and angles. This type of membrane is particularly useful where the membrane is below the level of the dpe in walls.

Bitumen sheets, which may be damaged on building sites, should be covered for protection as soon as possible by the screed or site concrete.

Bitumen solution, bitumen/ rubber emulsion or tar/rubber emulsion.

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These cold applied solutions are brushed on to the surface of concrete in three coats to a finished thickness of not less than 2.5 mm, allowing each coat to harden before the next is applied.

Hot pitch or bitumen.

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A continuous layer of hot applied coal-tar pitch or soft bitumen is poured on the surface and spread to a thickness of not Less than 3 mm. In dry weather a concrete blinding layer is ready for the membrane 3 days after placing. The surface of the concrete should be brushed to remove dust and primed with a solution of coal-tar pitch or bitumen solution or emulsion. The pitch is heated to 35°C to 45°C and bitumen to 50°C to 55°C.

Properly applied pitch or bitumen layers serve as an effective damp-proof membrane both horizontally and spread up inside wall faces to unite with dpes in walls and require less patient application than plastic sheet materials.