Damp problems

Damp on the lowest part of a ground-floor wall, with a horizontal tide mark and often salts in the plaster.

A damp patch on an inside wall that darkens after heavy or wind-driven rain, and dries back between wet spells.

You have been told the damp proof course has failed, and want to know what that means and whether it is true.

Low-level damp inside where a path, patio, flower bed or render outside has been built up over the damp proof course.

A white or grey bloom, fluffy crystals or a hard crust is coming through the plaster or the brickwork.

Staining, a brown tide or blown plaster on a chimney breast, often on an upstairs wall or in the loft.

Black speckling or patches on walls, ceilings, window reveals or behind furniture, often in corners and cold spots.

Skirting board that is soft, dark and crumbling, often with paint lifting and a musty smell at floor level.

A persistent damp, mushroomy smell with no obvious damp patch — sometimes with strands or a fleshy growth behind skirting or under floors.

Wet or salted cellar walls, water on the floor after rain, and a damp smell that reaches the rooms above.