Damp (structural) - Rising Damp

Rising Damp

Rising damp is the common term for the slow upward movement of water in the lower sections of walls and other ground-supported structures by capillary action. Although rising damp of up to 5 metres in height has been observed the height of rise is typically much lower and is rarely above 1.5m. Rising damp has been a widely observed phenomenon for at least two hundred years. Rising damp is deemed controversial because it is often misdiagnosed in buildings. Many misdiagnose a wall stain as rising damp instance due to misinterpreting the visual evidence of the wall and the readings of moisture meters. There is also strong evidence to suggest that it was a problem understood by the Romans and Ancient Greeks.

In simple terms rising damp occurs when ground water travels upwards through porous building materials such as brick, sandstone, or mortar, much in the same way that oil travels upwards through the wick of a lamp. The effect can easily be seen by simply placing a piece of porous brick, stone, or mortar in a shallow tray of water and observing how the water is absorbed into the porous material and is transported above the water line.

Rising damp can be identified by a characteristic "tide mark" on the lower section of affected walls. This tide mark is caused by soluble salts (particularly nitrates and chlorides) contained in the groundwater. Due to the effects of evaporation these salts accumulate at the "peak" of the rising damp.