It is important to be aware that there are different types of dampness with each having a different solutions. The types of dampness that you might find in your home are:
Rising Damp is caused by moisture rising up through porous masonry and is usually found in older buildings constructed without a damp proof course or where the existing damp proof course has failed or has been bridged. Moisture carries with it soluble ground salts, including nitrates and chlorides, which can be deposited into the masonry as rising damp evaporates. The effects of long term rising damp on your home can take the form of low level decorative spoiling and staining of paintwork and wall papers, plaster damage and salt contamination as well as the decay of timber skirtings, joinery and structural floor timbers. Rising damp is the result of capillary moisture and will therefore never take the form of 'free surface moisture' or 'water droplets' on a wall.
Remedial treatment of rising damp would normally involve the introduction of a chemical injection damp proof course using liquid silicone based materials or injectable 'mortar based' grouts. Severe dampness will also result in plaster damage and contamination and therefore replastering of the walls is generally required to provide a dry 'non-spoiling' decorative finish and to complete the system of damp control. The new plasterwork has an important function to perform and must be able to prevent hygroscopic salts passing to the surface from the underlying masonry substrate.
Lateral penetrating dampness
Lateral penetrating dampness normally occurs on external walls where the external ground levels are at a higher level than the internal floors and as a consequence dampness penetrates the walls fabric. A typical example of lateral dampness is in a basement where external walls are built against the external (subterranean) ground. Other causes of lateral dampness can be due to raised gardens and soil levels, flower beds, abutting garden walls, paths and pavements.
Methods of controlling penetrating dampness below ground level would depend mainly on the proposed use and the level of dryness required. Vertical waterproofing or tanking can take different forms and when applied correctly can provide dry walls & floors by either using cementitious slurries, water proof render systems or cavity drainage membranes.
Vertical penetrating dampness
Vertical penetrating dampness is caused by building defects and poor building maintenance. Roof defects, leaking, blocked guttering and downpipes, will contribute to the most common causes of dampness and are proven to be responsible for a high percentage of dry rot attacks caused on buildings.
Cracked rendering, defective pointing, external coatings and blocked cavities, along with inadequate window and door sealants are also responsible for moisture ingress, along with internal plumbing defects and poor external drainage.