'Chemical damp-proofing' may provide a useful barrier to damp. Electro osmotic damp proofing, if expertly installed, works in most situations. A damp proof course ( DPC ) is a physical barrier inserted into the fabric of a building to stop water passing from one place to another. This can be on a horizontal plane, stopping water rising up from the ground by being sucked up by the dry masonry above, or vertically to stop water passing from the outside of a building, though the masonry, to the inside. DPC's have taken many forms through the ages and one of the earliest forms was to use a layer of slate in the construction. Slate is still used but the less expensive plastic version is now more widely used.

Damp Proofing on Wikipedia
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