Dangers of damp: Do Your Boundary Walls Look Like This?
By Jurie Fourie, certified home inspector, The Home Detective
I took this photo during a client’s comprehensive buyer inspection. This wall had rising damp, falling damp and penetrating damp. In addition, the white marks on the wall were caused by efflorescence (read on for more explanation).
I often note how the maintenance of a property’s boundary, garden or courtyard walls are neglected. We should remember they that these walls protect our privacy and security and are our first line of defence against intruders, and so should not be neglected when it comes to maintenance.
The greatest enemy of these walls is damp, which can penetrate into the wall from below, above and from the sides of the walls. This article describes how to identify and treat, the different types of damp.
Rising damp occurs as a result of capillary action at and below ground level into porous masonry building materials. These materials are mainly concrete, bricks and mortar. The moisture rises up the wall in this way. It usually occurs where there is no dampproof course (DPC). Freestanding walls such as boundary and garden walls do not normally have DPC built into the walls because it would make the wall unstable. A layer of DPC would break the bond between the wall and its foundation.
The height to which the moisture will rise is determined by the evaporation rate and the nature of the wall. The normal limit for rising damp is generally about one metre above ground level.
Rising damp may show as a stain on the plastered and painted wall, the blistering of paint and loss of plaster. A damp area may be evident at the base of walls and in extreme situations, may cause the structure of the wall to wear away and crumble.
Falling damp is caused by downward water penetration from the top of porous masonry walls. This is as a result of the top of a boundary wall not being:
- adequately waterproofed, if at all;
- properly sealed at vertical expansion joints;
- repaired at copings that have cracked or deteriorating mortar joints;
- cleaned to prevent the build-up of dirt and moss on upper surfaces of stone or brickwork.
Leaves, bird manure, moss and dirt on top of the walls contain weak acids and salts which can promote decay of the masonry if absorbed.
Penetrating damp is a common form of damp. It occurs as a result of the horizontal ingress of water through gaps, cracks and joints in the wall’s structure. Penetrating or horizontal damp can be due to your or your neighbour’s irrigation system spraying against the boundary wall or foliage growing against the wall (bushes and trees). Other causes are deteriorating paint finishes and inadequately ruled joints which allows moisture intrusion into faced brick or stone walls.
Penetrating damp tends to produce localised patches of dampness and decay, whereas rising damp may affect the base of the wall.
Efflorescence is where an appreciable quantity of soluble salts is present in the masonry. It routinely occurs in masonry construction, particularly in brick and concrete. It typically occurs during the initial curing of the cementitious product. Moisture carries these salts to the face of the masonry or concrete where the moisture evaporates.
As the water evaporates, it leaves the salts behind as a white fluffy deposit. This deposit can normally be brushed off when dry. It usually disappears with time after rains or washing with water.
Efflorescence is generally an aesthetic concern and not a structural one. However, where there is excessive efflorescence, the crystallizing salts within the pores of the masonry can disrupt even the strongest material. As a result, this can lead to the breaking up and crumbling of the structure.
How to maintain your freestanding walls
Rising damp is not easy to resolve in the freestanding, boundary or garden walls because of the lack of DPC. However, you can do the following:
- Make sure that there is no ponding of water against the wall. Good drainage away from the walls is essential. If you have a low point in your garden against your boundary walls you will need to create a hole in the wall at the lowest point for the stormwater to drain away. Your neighbours have to accept a certain amount of your stormwater by law.
- Try not to overwater your gardens against boundary and garden walls. overwatering will result in sodden earth around the walls and, as a result, rising damp in the wall.
- Keep leaves and other debris on the ground which may retain water away from the walls.
- You should waterproof the tops of all freestanding walls with a layer of an acrylic waterproofing system or any other system to prevent moisture intrusion into the top of your boundary and yard walls.
- If there is a concrete or brick coping on top of the wall you must ensure that the joints form a water-resistant seal. You should seal all deteriorated joints or porous joints between the bricks and copings.
- Seal the top of expansion joints to prevent water from entering the joint with a silicone sealer.
- If your freestanding walls are plastered, check the paint finish regularly. It may be time to repaint if the finish is chalky.
- If you have a sprinkler system, make sure that you are not watering your boundary walls. Sprinklers heads are normally adjustable. If yours are not, change them.
- Trim bushes and shrubs so that there is a gap between the foliage, branches and the walls.
- If it appears that the moisture is from your neighbours’ sides, you will need to talk to them about the problem.
- Clean out and seal vertical expansion joints with a good silicone sealer. Any cracks should be sealed as well. Furthermore, if your plastered walls are covered in crazing cracking wash the wall down. Thereafter, when the wall is dry, seal the wall with a sealer and repaint the wall.
Efflorescence is caused by moisture absorbed in the wall evaporating and leaving behind salts in the form of a white powder. Therefore, if you repair and maintain your walls as suggested above you should have very little or no efflorescence appearing on your walls.