Rising Damp refers to a situation when moisture from the ground is drawn upwards through a permeable building material such as old brick or stone, by capillary action.
Rising Damp is very commonly misdiagnosed in older buildings, with some surveyors assuming that if there is no damp proof course, there will be rising damp, which is simply not true. This has resulted in numerous people wasting money on expensive damp proofing treatments when the money could have been spent on more effective measures.
It is normal for a small amount of moisture to be drawn into old brick and stone walls. The moisture dissolves soluble salts from the building materials and sometimes from its source. If the surface coverings of the wall are breathable, then the wall will have a large area from which any moisture can evaporate, and it will not cause a problem. You may just see the salts appear on the wall as a harmless floury substance which can be brushed away. However, if non breathable surface finishes are used, the moisture cannot easily evaporate away and you can end up with flaking paint and plaster, and even cracked stone or brickwork.
When there has been a long-term problem with moisture, evaporation at the edge of the damp area leads to a distinctive ‘tide mark’ as a result of salt deposition. If this mark appears near the base of a wall, it is often taken as proof of ‘rising damp’. However, this is wrong – you will get this tide mark from any damp. The most common reasons for damp at the base of the wall are actually defective ground and surface drainage, and condensation. (Condensation will appear on colder, lower regions of walls.)
For the moderate amount of moisture caused by genuine rising damp, the solution is to ensure that your surface coverings and pointing are breathable. This is discussed in more detail in our other advice pages.
If you have a serious damp problem, it is most likely not rising damp, or at least not exclusively rising damp. Make sure you know the real causes before rushing into expensive damp proof treatments.