Semi-rigid damp-proof courses - Mastic asphalt.

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Mastic asphalt, spread hot in one coat to a thickness of 13mm, is a semi-rigid dpc, impervious to moisture and water. Moderate settlement in a wall may well cause a crack in the asphalt through which moisture or water may penetrate. It is an expensive form of dpc, which shows on the face of walls as a thick joint, and it is rarely used as a dpc.

Mastic asphalt or pitch mastic.

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These materials are spread hot and finished to a thickness of at least 12.5 mm. This expensive damp-proof membrane is used where there is appreciable water pressure under the floor and as ‘tanking’ to basements as described in Volume 4.