Rising damp – and what to do about it

Whether at the coast or inland, rising damp is a problem that affects many South African homes. Luckily, there are ways your customers can solve this problem themselves, although sometimes it’s best to call the experts. 

Rising damp is more common in older homes, where proper preparation methods including a rising damp barrier, weren’t used when the house was built. It occurs when water infiltrates the capillaries in bricks from the ground and defies gravity to travel upwards, causing damage. This then extends to any plaster, wood or other treatment surrounding the bricks. The added danger is that salts within the earth can also be absorbed upwards, causing further havoc. It’s easy to spot rising damp because it leaves a tide-mark-shaped stain on the wall and usually doesn’t travel further than 1.5 metres up a wall. It’s something that should strike fear in every homeowner because it can cause structural damage and is often costly to fix.  

The causes 

• When building takes place, most homes have a barrier installed on the lowest level that is made from water-resistant material, such as bitumen, slate or plastic, and is intended to prevent rising damp. Unfortunately, sometimes this can fail (or be non-existent, in the case of an older home)  
• A leaking pipe can also be the cause of rising damp 
• Sub-floor ventilation that isn’t properly ventilated can cause a build-up of humidity
• Poor drainage. If pipes or guttering aren’t working properly, water might gather underneath a house and not be absorbed properly. 

Identify the risk 

The sooner rising damp is identified and treated the better because if left for long periods of time, the problem just becomes exacerbated. Ask your customer to bring in a photo of the problem, so you can advise them on how to treat it. 

 Consumers should look out for: 

• The tell-tale tidal-shaped mark on a wall 
• Any other visible signs of moisture  
• Musty and damp smells 
• Plaster, paint or wallpaper deteriorating from the base of the wall upwards 
• Decaying timber in skirtings or floorboards 
• Mould 
• The rusting of fasteners made of steel 
• White salt stains on the wall. 

The dangers 

Not only is rising damp likely to cause structural damage, but it can also have other effects, such as being detrimental to the health of homeowners because of the resultant mould and mildew. When it comes time to sell, rising damp will depreciate the cost of a home.  

Rising damp versus condensation 

It’s important that rising damp is correctly identified and not mixed up with other issues, such as condensation. The only way to really prove the difference is to gather samples of mortar from different levels within the wall. If it is condensation, the damp would not have penetrated into the heart of the mortar. If it is rising damp, it will be wet right through. 

How to fix it 

Mild cases of rising damp can be fixed by amateur DIYers. They will need a scraper, plaster primer, damp seal, paint and a paintbrush. 

Step One: Scrape the wall where there is visible bubbling or peeling. Remove all the paint from around this area.  

Step Two: Use the damp seal to cover this area. It must be covered completely, and there must be no gaps. It might require two coats. 

Step Three: Once the damp seal has dried, use the plaster primer to cover the area, ensuring any cracks are properly sealed.  

Step Four: Use the paint and paintbrush to repaint the wall.  

A more in-depth solution 

Severe cases of rising damp shouldn’t be fixed by amateur DIYers. If you have customers explaining what sounds like an extreme problem, be sure to rather recommend they contact professionals who can assess the situation and treat it accordingly. However, those with a little more DIY experience can attempt to fix the issue themselves. 

The most successful fixes on the market for severe cases tend to be chemical injection creams, that are inserted into holes in the wall by hand. Once inside, the cream will become more liquid and penetrate the bricks, absorbing moisture. It will then turn into a waterproof barrier, preventing water from rising any further. The wall will have to be replastered thereafter, and it’s essential that high-quality mould and dampproof paint are used. 

Step one: Chip away the wall from the base upwards, until the brick and plaster, is completely exposed. 

Step two: Drill small holes in the bricks about 7-8cm apart.  

Step three: Squeeze the damp-proof cream into the holes and allow it to dry overnight. 

Step four: Use waterproof plaster or mortar to cover up the holes. Don’t repaint for a few weeks, until you are satisfied that the problem has been resolved. 

Another (more expensive but sometimes necessary) solution is the installation of a new membrane at the base of the wall. It is labour-intensive and time-consuming and should only be done by experts.