All About Rising Damp

Rising Damp?

Rising damp in walls is when capillary action causes the upwards flow of moisture through a permeable wall structure. This moisture rises through the pores (capillaries) in the walls which causes the masonry to act like a sponge. It’s the same capillary action that plants use to absorb moisture through their roots. Rising damp varies in severity depending on of several factors including the level of groundwater, the pore structure of the masonry materials (brick, bluestone, sandstone, mortar etc…) and the rate of evaporation away from the wall surface. Normally it is present in the bottom of the wall and rarely goes above 700mm above ground/floor level. When present it requires to be treated because if left it will have a damaging effect on the structure of the building. Like cancer in humans the longer it is ignored the more severe the consequence.

Rising Damp, Rising Salt Damp or Salt Damp?

Rising Salt Damp, often referred to as Salt Damp, occurs when salts are present in the soil and are drawn up with the rising damp. In South Australia it is commonly known as Salt Damp due to the salinity of the soil in that state. Salt Damp is more destructive than rising damp as once the salts are present, they continue to attract air born moisture on humid and/or damp days which causes them to expand and then contract on dry days eventually causing crumbling of masonry and mortar with potentially serious consequences. Salt damp is more visually obvious as evidenced in white crystals on the surface of masonry and render near the bottom of the wall. Both Salt Damp and Rising Damp can be treated with our Dryzone and Dryrod eradication systems with 100% certainty and peace of mind. How do you know if you have Rising Damp?
  1. Decorative Spoiling – Rising Damp and the accompanying salts can cause plaster ro deteriorate and paint to blister.
  2. Erosion of the Building Fabric – Ground salts introduced into the wall by rising damp can attack and dissolve the binders in brick, stone, and mortar causing them to lose their strength and structural integrity. Crystalising salts can exert such forces that the mortar, brick, stone microstructure is destroyed.
  3. Increased Heat Loss – Dampness in porous building materials causes a reduction of insulation properties as air in the pores is replaced by more conductive water. The thermal conductivity of a wet brick has been found to be approximately twice that of a dry brick. Not only does this increase the risk of condensation but increases winter heating costs.
  4. Health Effects – It has been widely documented that excessive dampness in buildings can have negative effects on the health of it’s occupants.

If any of these symptoms are in evidence then there is the risk of rising damp being present. However a process of elimination is required as other cause of dampness in buildings need to be eliminated as they require other remedial treatments.

N.B. Always consider the above as possibilities if the house is less than 40 years old.

Having identified the cause of moisture is rising damp then it needs to be treated by introducing a new damp proof course. Sanding back damaged walls and/or plaster and repainting, covering the wall with plasterboard and any other band aid remedy will prove to be both a waste of time and money as the problem would not have been resolved. There is some urgency introducing a new damp proof course at this stage as rising damp in masonry is like cancer in humans, the longer you leave it untreated the more serious the condition especially if salts are present as evidenced by white powder on the surface. The reason the salts cause so much damage is that they are continually moving. On dry days with low moisture in the air they contract then on wet days or days of high humidity they expand so they are continually expanding, contracting, expanding, contracting until the masonry starts to crumble and mortar turns to dust.

How long does this take? Who knows as there are many variables, it could be years or tens of years but it will happen unless treated.