What is rising damp?

Rising damp is a major issue with house construction and can cause many problems. The major question, however, is: what is rising damp, and what can be done about it?

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The Damp Proofing and Waterproofing Association of South Africa defines rising damp as a condition where moisture from the ground travels up through the pores in the bricks and mortar of a building, much in the same way that oil travels up through the wick of an oil lamp – once rising damp has become established, this moisture can cause problems such as damp patches on walls, peeling paint/wallpaper and eventually plaster falling away from the wall. In the longer term, it will lead to structural damage to the building, if left unchecked.

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The symptoms of rising damp can often be confused with the symptoms of other damp problems such as lateral damp and condensation. These types of dampness require different methods of treatment, so it is essential that an expert is consulted to diagnose the type of dampness to be treated.

Hygroscopic salts are made up of chlorides and nitrates. These salts attack the cement and sand, mortar between the bricks and the bricks and plaster on the walls. These salts multiply and expand with moisture in the air and cause the masonry to crumble and eventually structural failure will occur.

Reasons why rising damp has occurred at home

The problem of rising damp has been known for at least 100 years. Therefore, it has been common building practice for some time to install a damp proof course (DPC) whenever a house is built. In a typical solid floor construction, the DPC usually consists of an impervious barrier around the whole building, set into the mortar bed just above the floor level. This DPC can become ineffective for a number of reasons:

  • The original builder forgot to install a DPC.
  • The original DPC was not positioned correctly.
  • The original DPC has deteriorated due, for example, to house settlement, vibration, from passing traffic, or general land subsidence. This is especially common where a Bitumen DPC has been used.
  • The damp course has been “bridged” e.g. by earth being piled up against an outside wall.

If the rising damp is to be eliminated, it is essential that the precise cause of the breakdown in the DPC is established. Once again, expert advice from DWASA should be sought.

Causes of rising damp

Causes of damp and the causes of rising damp are varied and numerous. They include high humidity or excessive condensation levels in the home, combined with poor ventilation and/or faulty drainage facilities. The appearance of damp often indicates a multitude of problems rather than a single source, but there are still several causes of damp you can look out for to help reduce the risk of it taking over your home:

  • Closed doors and windows trap heat and regularly result in the build-up of excessive moisture and consequently mould and damp. To prevent this from occurring, remember to keep the home well aired; even in the cooler winter months doors or windows should be opened for at least an hour a day.
  • Excessive amounts of baths and showers can also result in a build-up of humidity, which if lacking an escape route also ends up manifesting as damp or mould in the property. If you have a large family and a small home, remember to keep bathroom windows open for as long as possible and try to stagger showers throughout the day if you can.
  • Over-using electrical appliances, such as the oven, washing machine or dishwasher can result in large amounts of heat being produced in a relatively short amount of time, especially if they are all used at the same time. To keep heat levels down stagger appliance usage and remember to turn everything off after use.
  • Drying clothes indoors, such as on radiators or ‘clothes-horses’ can increase the moisture levels in the home too, especially if the heating is on. Try to hang washing outdoors whenever you can, as even cold winds will dry things quicker and more effectively while also reducing the humidity in the home.
  • Make sure your damp proof course (DPC) is in good condition. A DPC is a thin layer of waterproof material which is inserted horizontally near the bottom of a building’s structure to prevent damp rising up through building materials. Liquid DPCs can also be injected into the walls of your home by a damp treatment specialist. A defective damp proof course is a major cause of rising damp, so make sure yours are in good condition.
  • Finally, check for broken gutters or downpipes outside to see if they are causing leaks that could be letting water into your home. Increased internal moisture often causes damp which, once it takes hold, can be extremely difficult to deal with.

If rising damp has occurred in your home, the Damp Proofing and Waterproofing Association of South Africa should be contacted so that a course of action can be decided. Damp can cause major issues in the home and should be attended to as soon as it is found in any structure.

Sources: Damp-proofing & Waterproofing Association of South Africa and Service Magic

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