Waterproofing Walls

Water and dampness in walls and how to repair them

See also:

• Rising Damp
• Concrete roof gutters and aprons

Golden rule - stop the water getting in

The golden rule in waterproofing is to stop water getting in and not to try and stop it getting out. This sounds pretty obvious doesn't it but you'd be surprised at the number of even experienced builders who start trying to seal leaks from inside. Mind you, finding the point of entry may not be easy, water can travel a long way through a structure or even saturate it completely making finding the source a difficult task.

Why do we get leaks

The walls of most buildings these days have reinforced concrete vertical columns with reinforced ring beams along the top that provide the strength. The areas between the columns and beams has an infill of light concrete blocks or soft local red bricks with a skim of hard concrete on the surface. The reinforced concrete is often very poorly made with cracks and cavities in it and the infill is like blotting paper (sorry you might not remember that, like a sponge).

This sort of structure is very rigid and the regular earthquakes we get in Bali (yes we get lots, usually so small we don't even notice them but now and again one that will wake you up in the night) and these regular ground movements result in cracks in structures usually through the walls of buildings.

It is also very rare to find a tradesman who will work logically through the symptoms of a problem and accurately identifying the cause rather than taking the easy way out and treating the first thing he sees.

How do we stop water getting into walls?

So we have water in a wall, we have kicked the cat (repeatedly) and taken to drink.

So how do we deal with?

First check into a detoxication centre to deal with our alcoholic escapism, this will stop the DTs and the bloodshot eyes.

Next check into an ashram. Take a 9 month course in transcendental meditation where we learn love for all living things (including cats) and acceptance of the water issues in our lives.

Finally get a shave and a soothing massage.

Now we can return home, apologise to the cat, hide the bottle of gin and start thinking about our wall.

First - find where the water is getting in

As we all know, it is a basic law of nature that water flows downhill so we start at the highest point.

Is the wall open to the elements at the top or is the roof overhanging? If the roof is not overhanging look along the top of the wall and check for cracks, even very fine cracks. Does the upper surface have a waterproof coating. Is there a concrete roof or a parapet wall? It may be that water is getting in where the concrete roof slab meets the wall or through the parapet wall and into the top of the wall below.

Leaks from cracked concrete roof gutters

A very common problem in Bali is leaking concrete gutters. It is regarded here that it is very bad form to allow water from your roof to run off onto a neighbour's property or into a street. If a building is built right against the property line, and very many are, then usually a concrete gutter is built along the top of the wall to catch water from the roof and take it away. These concrete gutters have two basic problems:

1. Ground movement often results in cracks across the gutter which allow water into the wall. If the cracks are small this can be fairly easy to fix. The gutter must first be cleaned thoroughly then waterproofed in the inside, it is best to do the whole gutter while you are at it.
2. Wall gutters are often built with the outer wall higher than the inner wall so that if the gutter fills with water it will overflow into your building either across the ceiling or down the inside of the wall. In Australia roof gutters are made of plastic or aluminium and purposely have the outer side of the gutter lower than the inner side so if they fill up they will overflow outwards. To solve this problem firstly make sure that the drain pipe from the gutter is large enough to take the roof area it has to drain and that the outer side of the gutter has low points cut in it to provide overflow points. These should, of course, be lower than the inner side of the gutter. It is also a good idea to make sure that downpipes have a gap between the gutter and the ground so that water cannot backup in the pipe.

Check the surfaces of the wall

When you have checked along the top of the wall next look at the surface of the wall. Carefully check it from top to bottom. Is it open to the weather. Note that if you are in a windy place the wind can drive rain at steep angles against the wall. Sensibly designed buildings have good roof overhangs which are designed to keep rain off the walls. Roof overhangs also keep sunshine off walls and so keep inside room temperatures down.

If you have a wall exposed to rain you can waterproof it to stop water getting in. Take particular note of any cracks in the wall which will need special treatment, we'll come to that in a minute.

A word of warning, a wall needs to breath so that if water does get into it it can evaporate out again. Do not waterproof both inside and outside surfaces of a wall. If you do you may well always have damp walls.

Rising damp

The last thing to check for is rising damp. This is very common in Bali where damp proof courses are not installed but it can be fixed if you know how. Like poaching an egg this is not something you would trust to people who don't know what they are doing. The solution is to cut out a horizontal slit right through the bottom of the wall and full length of the wall, yes this needs great care and for obvious reasons you don't do it all at once. You then fill the slit with high density cement. This is known as a sloof and will stop water rising up inside the wall from the ground beneath. Techniques widely marketed in Britain (usually of very dubious efficacy) such as injecting silicone solutions are not available here and would probably not work because of the high porosity of the batako blocks in the walls.

Sealing the leaks

Alright so we have found the cause, how do we treat it? The traditional method is to use a skim of high density waterproofing cement but this is not a method I recommend. This type of waterproofing film is very brittle and can crack. On a surface exposed to sunshine the excess surface heat will crack the concrete skim away from the wall beneath allowing water to enter which can travel between the concrete skim and the surface beneath.

My treatment of choice is a thick polymer paint applied with a brush. It comes in different colours. There are cheaper local versions but I suspect you get what you pay for. Cracks need special treatment as they are likely to suffer further movement. Raintite comes with a membrane material, rather like a thick bandage. Paint the Raintite polymer along both sides of the crack, stick the bandage over the crack along its length then paint the bandage to fully saturate it with the polymer. If the crack moves the bandage will stretch a bit and maintain the waterproof film. It should be noted that these polymers do not like water.

Before applying a waterproofing polymer it is essential that the surface is very clean and dry. Any loose paint, moss or dirt must be removed first and the surface must be dry. Wait for a day when the surface and any cracks have fully dried out before you waterproof.

For general waterproofing of walls in good condition Dulux Weathershield is the universally respected waterproof paint for outside walls but again, make sure the wall can breath.

Now we have dealt with the difficult stuff we can move on to easier things like teaching a chimpanzee how to poach and egg.

See also:

• Rising Damp
• Concrete roof gutters and aprons