Rising Damp – it is enough to put a home owner into a spin, as they watch the process of dampness and salts rising from the ground to eat away at their home. This process occurs as moisture is drawn into mortar and masonry materials by the process of capillary suction.
It is the same process as putting water into a container and then placing a sponge in that water. The effect of capillary suction resulting in the sponge taking on water.
Masonry has fine pores, small fissures and cracks and just like the sponge, ground moisture will be drawn upwards through these against the force of gravity. That leads to the base of the walls becoming damp.
The height that the moisture will be drawn can be dependent on the absorptive qualities of the bricks, stone and mortar. It can also be dependent on other factors such as the height of the water table, drainage wall thickness and the rates of evaporation.
Similarly, salt attack occurs when soluble salts from this ground moisture are carried into the wall with the water and form crystals within the pores of the masonry. Through the process of moisture evaporation these crystals will continue to grow and disrupt the masonry further causing fretting and damage to the masonry surface. Repeated cycles in the weather of wetting and drying will lead to rapid crystallisation of the salts and further intensify this damage.
Rising Damp and salt attack occurs in buildings, where there is a lack of a damp proof barrier at the base of the wall. It may also appear where the damp proof barrier has been bridged (covered). If there is high salinity in the soil, or a high water table, then salt damage will be even more rapid.
A visual inspection for rising damp and salt attack will normally appear internally as blistering or bubbling paint and plaster near the base of the wall. Often there is a dark stain or tide line above the skirting boards.
Externally mortar will crumble and become powdery between bricks and stones in lower courses. In severe cases bricks and stones will be eaten away and must be replaced.In treating damp issues it is important to firstly have the problem diagnosed by an expert. They will identify where the damp is coming from and the extent of the problem.
Often a damp problem is not rising damp but has been caused by other moisture issues. A leaky pipe or a gutter failure that may only need some maintenance attention to fix. It could also be something as simple as increasing the sub-floor ventilation or lowering the paving around the outside of the building to rectify an issue.
Remediation will vary and is often dependent on how high the damp is and how severely the salts have attacked the wall. An independent expert, building inspector or salt damp technician will be able to recommend an appropriate course of action.
For DIY Information please see our next blog in the Series – How to treat Rising Damp and Salt Attack