In order to fix damp, firstly you must ascertain what type of damp you are dealing with, the extent of the problem and the cause or causes.
The cause is very important and the treatment can vary immensely depending on what has caused the damp. If the area is suffering from penetrating damp then fixing could be as simple as having a pipe leak repaired or a defective gutter in need of repair or maintenance.
Whereas dampness can also be caused by a lack of effective ventilation, this can cause condensation, which can result in the build-up of water droplets usually around windows and in corners of rooms.
This generally affects external walls as they are cooler and the treatment for this would be improve the ventilation, either by simply opening windows etc or in severe cases, you may need to have a ventilation system installed.
Remove moisture from the room
The outcome of such an installation would be the removal of the excess moisture from the room and therefore with better airflow the condensation is avoided. Where the walls are affected by rising dampness, this may be caused by a defect to the physical damp proof course installed at the time of building, usually due to the natural movement of a property over time or may be due to bridging of an old damp course.
Treatment for rising damp is more complex in that it requires the removal of the wall plaster to expose the brick work in affected areas. Once the brick is exposed the walls are drilled at the mortar base and a new chemical damp proof course is injected into the wall. Where necessary, when a treated and untreated wall adjoin, a vertical damp proof course is also created to provide maximum protection.
Once the new damp proof course is in place the walls are replastered using a rendering plaster which includes salt inhibitors and waterproofing agents to provide yet another level of protection . When complete, walls are skimmed to provide a smooth finish ready for the final stage of re-decoration to the wall after drying out.