This leads to a path for rising damp to penetrate past the Damp Proofing. This is important in areas with a high water table, particularly if ground waters are at all salty (see diagram below).

II. Not Sandwiching the Damp Proofing Between Wet Mortar

It is wrong to lay Damp Proofing on the concrete slab or brickwork without providing a seal between the materials. When there is no seal - a capillary path will open up, allowing rain penetration except in highly loaded situations. Mortar is a very good sealant. The Damp Proofing should be sandwiched between wet mortar (see diagram below).