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Damp queries

Damp wall

I built a house in 2007 and moved in during April 2008. We need to repaint the house and have found damp spots on the bottom floor inside, limited to the external walls. There is no damp on the top floor inside external walls. The foundations have damp course and there is no damp on the outside walls. We used cement stock bricks and plastered all the walls. Plaster primer was applied before painting all walls. What is causing the damp and what should we do before repainting?


Toni Stella, our paint expert, replies: 

Reading the above problem I assume that the house is a double storey as you found damp spots on the inside walls on the bottom floor and no signs of damp on the top floor. I’m also assuming that the exterior walls are plastered down to ground level. We are also in agreement that you have a damp problem. But what is causing the damp?To correct the problem, you need a qualified person who will use the correct equipment to diagnose the cause of the damp and who will know how to rectify it before applying any primer or waterproofing compound.I have outlined a few reasons why damp and rising damp occurs:


* The failure of an existing damp proof course (DPC) bridging due to the raising of external ground above the DPC on the exterior of the wall.

* Some bricks, stones and plasters are porous, allowing the damp from the ground to rise by capillary action, carrying with it ground salts including chlorides and nitrates.

* During the building stage the DPC was damaged or not correctly welded together to create a continuous barrier.

* Water irrigation system too close to the exterior walls.


NB: Where exterior walls are plastered to ground level, the damp could rise approximately 1m the major paths through which the water rises are the mortar beds, suvh as the mortar between the bricks. For water to get through the wall it must cross the mortar bed to damage the paint coating.The primary task of the investigator is to correctly identify the source of dampness. This is best achieved by a process of investigation and elimination. Extreme care must be taken, for example, in the winter months to eliminate condensation as one of the potential causes of dampness.


Therefore, to provide a ‘dry’ wall and a suitable surface to take new decorations, the Safeguard Damp-proof Course Systems involve two fundamental processes:1. The insertion of the chemical damp-proof course.2. The removal of old, contaminated plasterwork/decorations and replacing with specialist re-plastering to prevent the passage of any residue moisture and contaminant salts from passing to the new surfaces from underlying masonry.I have also been informed that an area in Centurion has an underground water belt, which rises due to excessive rainfall. Perhaps you could investigate this with your local authority.


Contact Toni on 082-781-9669 for further information.

Removing mildew stains from a ceiling
I am need to remove mildew stains from my bathroom ceiling. I tried a mixture of Jik and water but this only worked for a short period. Are there any other solutions?
Ashwin Rampersad, by email

Toni Stella, our paint and coatings expert, replies

New information has come to light that, in fact, Jik may not be the solution removing mildew. It seems Jik simply bleaches the mildew stain, which is why the stain reappears. Use a fungicidal wash, such as Mould-Buster from Tile and Floor Care, or Mould-Stop from Tile Doctor, which destroys the bacteria in mildew. 

Mildew in bathrooms is a common problem caused by moisture and damp and can easily be solved by installing a ceiling fan. You should also check the ceiling area and roof for possible leaks and rectify this before cleaning and coating the ceiling as follows: 

Step 1: Lay down drop sheets to protect the bath, basin and toilet.
Step 2: Wear safety goggles to protect the eyes. 
Step 3: Remove all loose flaking paint, if there is any, using a steel brush and scrapers, and sand down.
Step 4: Sweep or vacuum dust and any other dirt from the floor before painting as this will also spoil the job.
Step 5: Scrub the ceiling with an anti-fungicidal wash, such as Mould-Buster or Mould-Stop, using a hard-bristled brush and thoroughly work the solution into the ceiling, allowing the solution to penetrate into the spores. Leave overnight to allow the solution to kill all the bacteria in the mildew or mould.
Step 6: The next day, scrub again using a hard-bristled brush. Using a clean cloth and fresh clean water (a spray bottle works very well), wipe off all residue until clean, then dry the surface with a clean cloth. 
Step 7: Skim damaged areas and sand down.
Step 8: Apply a coat of pigmented plaster primer, diluted 20 percent with turpentine, using a mohair roller. Allow to dry for 18-24 hours.
Step 9: Apply a coat of Universal Undercoat and allow to dry for 18-24 hours.
Step 10: Apply final coat of polyurethane enamel, such as Plascon Velvaglo or Dulux Pearlglo, and allow to dry for 18-24 hours.

A common problem when using PVA water-based paint in bathrooms, showers and kitchens, which are prone to damp caused by steam, is that PVA contains cellulose thickeners that promote the growth of bacteria and fungi, causing mould and mildew. We therefore recommend using oil-based paint instead.

If the bathroom has no air bricks, try to ventilate the room by opening windows or install a small extraction fan.

For further information, contact Toni on 011-622-4852 or 082-781-9669.

Mike Howis
My bathroom ceiling keeps getting black spots, which I think is a fungus or mould. Somebody suggested cleaning it with vinegar and water and it got rid of it for at least a month, but it has started to come back again. The ceiling was painted with Dulux 65. Is there any other kind of fungal paint that can be used? The bathroom is well ventilated after bathing and there is an extraction fan with an air brick above 200mm away from it, which is just under the ceiling.

John Reid - Dulux
The common reason for ceiling mould is humidity and lack of ventilation. We would suggest that you use Dulux Wallguard on the ceiling. Firstly, clean the ceiling thoroughly using swimming pool chlorine to the ratio of one tablespoon to one litre of water and apply using a brush and wait for two days before applying the paint. Please note that you should wear eye goggles and gloves whilst applying the chlorine.

Down with rising damp
We seem to be fighting a losing battle with rising damp in our house. I have lost count of how many times I have scraped down, damp sealed and painted these walls. We even dug a 'French drain' system outside one length of the house; this seems to have helped about 95 percent. The problem is in the children’s playroom, on the other side of the house where I can't install the French drain system.

My kids want to sleep in the playroom during the holidays, but they then get sick due to all the spores and damp from the wall. We were thinking of decorating Masonite board and sticking it against the wall, or putting tongue and groove pine boards against the wall. We know that it will eventually rot, but it will provide a temporary (maybe four-year) solution. We have seen these little bricks that you put on the wall, what do you think of those?

We need something that we can preferably do ourselves, in our own time – especially because we live in a little town and experts would charge travel fees.
Belinda Spence, Escourt

Sharl Bennie, our building expert, replies: 

This is one of the most difficult problems with which to deal. There are a number of things that can cause this problem, and some of them are very costly to address and, often, the solution is only temporary. 

Regarding the French drain that you installed – does it take the water away from the building and allow it to run away into the drains or perhaps into a garden some distance away? If not, this drain will only become an underground pond.

I have found that water does this because it needs to vent so that it can dry out. The wall becomes a conduit for underground water/moisture to find its way to the surface so that it can dry out. This is why it rises up the wall, and it will continue to rise until it gets to a point where it can vent and dry out. 

What I have done with quite a lot of success is to make cut-outs in the outer brick wall and install airbricks into the cut-outs. These cut-outs do not go right through the wall, but rather just deep enough for the airbrick to fit into the cut-out and be flush with the wall. Cement the airbrick into the wall around the edges only, and, when you paint the airbrick, do not paint right inside the holes onto the brickwork behind. These airbricks should be placed about 300-500mm above ground level and about 800mm apart, all along the problem areas. This allows the wall to breathe and the damp will gravitate towards the airbrick where it can vent and dry out. 

Remember that it takes a long time for a wall to dry out and you should wait a month or two before you seal and paint the wall again. Watch for water pooling against the building, this will aggravate your problem – make sure that the drainage away from the building is very good.

I have noted over the years that when damp sealing is done on a wall, a process of removing the plaster and exposing the brickwork is used. A silicone is injected into each brick in the lower line of bricks in an attempt to create a damp course seal, and then the wall is plastered with a waterproof admixer, such as DampLoc, in the plaster. This works very well for a couple of years and then you will see the damp pushing through just above the joint in the plaster. It is not a long term or permanent solution and it does come with a price. For me, constructive venting and diverting of underground water has been more successful.

Contact Sharl on 082-554-1921 for more information.

Rising damp and wall plaster
I am adding onto an existing house which has wooden floors. The walls were plastered to below ground level (below floor level). There is no rising damp problem on the plaster.

I want to do the plaster work in the same way in the new room, but am concerned that damp will rise as the new room has a concrete floor. The new room is being built with cement bricks (not blocks).

With what can I treat the plaster below floor level to prevent damp rising up the plaster as I have seen happening in other houses? 
Eric Whittal, East London

Cindy Engels from A.Shak replies: 

The best way to prevent rising damp is to use a product manufactured for this purpose. Our DampLoc or Plascon’s Dampseal are suitable. These products can be applied to the bricks before plastering, or over the plaster before painting. An alternative is to use an additive, such as our TileLoc, which can be mixed with cement to form a paste-like product, and paint this on before the plaster is applied, or over the new plaster to form a waterproof membrane.

Contact Cindy at A.Shak on 011-822-2320 for more information.

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