Building Construction, Renovation & Maintenance

Rising Damp

Rising Damp

Rising damp is a very common problem in many parts of the world and can result in dampness throughout a building. Rising Damp is not difficult to repair but it does require tradesmen who know how to tackle the problem. What causes rising damp, how do we recognise it and how do we repair it? We also look at methods that do not work.

See the full Fixed Abode article "A Case Of Wrinkly Feet" here

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serious rising damp in a wall

What is Rising Damp?

Rising damp is an exasperating but very common problem particularly in damper climes such as monsoon areas of the world, it is rather difficult to get rid of but, using the correct materials and an engineered technique, rising damp can be very effectively removed.

Rising damp is moisture usually in the lower parts of walls (less than 3 feet up the wall unless the wall is tiled in which case it may be higher.

What causes Rising Damp?

Rising Damp is caused by Surface tension and capilliary action. It is all to do with that skin on the surface of water.
“Skin?” I hear you say. Well yes, it's like a skin. Water doesn't get on very well with its neighbours you see, in fact it gets quite stressed. Oh the middle bit is all right but that bit at the surface can't cope very well at all, it suffers a condition known as surface tension.

We all know that if you put water in a glass with dry sides the edge of the water curves down where it meets the glass, in a wet glass the edge curves up, it's a meniscus sort of thing. In a confined space such as a hole or a crack the surface tension pulls the water through. This is, of course, known as capilliary action and is what makes a wick work as in “this bloke going on and on about rising damp is really getting up my wick.”

In a wall that is permeable, such as one made of brick or light concrete batako, capilliary action allows water to soak up the wall like a sponge. It will rise as high as a metre above ground level.

How do I know if I have rising damp?

Take off your shoes and socks, now are your feet white and wrinkled? No? Ok look along the lower part of your walls. Usually in the lower 30 cms you will find blistering paintwork or damp patches. The blisters often peel off leaving concrete or a white chalky plaster showing. Depending on how serious the problem is you may find damaged paintwork up to a metre up the wall.

Damage may be particularly evident if the ground or floor level is higher on one side of the wall than the other.

Note that in some countries walls are generally concrete with a very thin skim of chalky white “plaster”. Do not be mislead this may not be plaster as European people would expect, it is only a very thin skim on a very hard concrete render. Try putting a picture hook in the wall and you will quickly develop a rather distasteful absence of humour and a very a bent nail.

typical rising damp in a wall

So how do we deal with rising damp?

First let us talk about what you do NOT do.

Rising damp is a common problem in the UK and other damp climates across the world. In many of these countries there are thriving industries providing “solutions” for rising damp. “Solution” is rather an abused word and it is amazing the number of snake oil salesmen who are drilling, wiring, squirting and coating their way through peoples houses, often at large expense and with a remarkably high level of failure.

The most common solution people use is to waterproof render the wall up to a height of a metre on both sides.


Waterproofing the surfaces of a wall does not work

A wall has to breathe if it is to dry out. The waterproof coating does not stop the water rising inside the wall but it does stop it getting out. A good friend of mine waterproofed his walls to a height of a metre and the result was that the damp rose even higher and he now has damp patches as high as one and a half metres up his walls.

Tiling walls does not solve the problem

In Indonesia many people tile the lower part of their walls to solve the problem. This does not work for the same reason as water proofing the wall (above). It is, in fact, far cheaper but far more effective to carry out the correct repair work

Injecting silicone usually fails

Another common “solution” involves the injection of silicone or other waterproofing substances into holes drilled in the wall. Sometimes these methods succeed but usually they fail because there is not a continuous barrier along the wall. These methods often also include injecting expanded polymers into the wall cavity – also not a good idea because it stops the air circulation inside the wall cavity. This is not relevant to us because to date I have not yet come across a cavity wall in Bali apart from house walls that back onto someone else's house in which case the cavity is usually disastrously filled with builders rubble, also not a good idea.

Electric currents in copper wires doesn't work

Another marketed “solution” involves installing a copper or titanium wire along the bottom of the wall and applying an electric current. A trial of this technique was carried out recently in Bali. Guess what – it failed.

So what can we do?

How to stop rising damp

Install a damp proof course or an impermeable membrane

The standard way of preventing rising damp was commonly used by the Victorians. More than a hundred years ago houses were built with a thin layer of impermeable slate right through the wall about two or three inches (those were those strange measurements the Victorians used) above the ground. Known as a damp proof course it was very effective and is standard building practice to this day although instead of slate a broad bituminous or plastic tape is usually used.

Unfortunately in many parts of the world damp proof courses are not built into house walls and hence there is a common problem with rising damp which is evident in many, many houses.

An effective solution for installing a damp proof course in an existing wall involves cutting a slot through the wall and inserting an impermeable tape. Shims and wedges are needed to support the wall until it is grouted up. Unfortunately this system is not currently available in Bali.

Probably the best method to use is to install a waterproof band.

The bottom few centimetres of the wall are replaced using high strength concrete with waterproofing additives. This band must cover the full length and width of the wall to provide an impermeable band just above the floor. If the ground or a concrete floor are higher on one side of the wall the sloof must be continued between the ground and the wall to ensure a continuous barrier.

It sounds drastic but is surprisingly painless and not expensive - unless you have marble wall tiles of course. A sloof follows the sound logic the Victorians used.

As a final comment if you are building a new house and you specify a damp proof course don't expect one to be installed. Even if the builder did know what you are talking about suitable materials are unlikely to be available. The best bet is to specify an effective waterproof membrane at the building stage and check to make sure it is installed.

Rising damp can be beaten but beware of smooth talking salesmen with fancy products and follow traditional techniques.

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Copyright © Phil Wilson June 2008
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