Capillary damp in walls – causes, diagnosis and drying

Capillary damp is one of the commonest problems in buildings. It usually appears at the bottom of a wall and works its way upwards. Damp patches, white salt deposits, flaking paint and crumbling plaster can all show on the surface.

The problem is not only a visual one. If the cause of the damp is not established and dealt with, the plaster and other parts of the building can be damaged over time.

Not every damp patch is capillary damp

This matters.

A damp wall can be the result of:

• a concealed leak on the water supply;
• a leak from the drainage;
• water penetrating an external wall;
• a problem with the waterproofing;
• capillary rise of moisture;
• condensation;
• another source of moisture.

It is therefore wrong to label every damp wall „capillary damp“ automatically.

The cause has to be found first.

What is capillary damp?

Capillary damp is water from the soil, or from damp parts of the structure, penetrating the pores of the building materials.

Masonry contains a great many small pores and capillaries. Under certain conditions water can travel upwards through them. The phenomenon is known as capillary rise of moisture.

It is seen most often in:

• older buildings;
• houses and ground-floor rooms;
• cellars and basements;
• buildings with damaged or missing waterproofing;
• buildings whose horizontal waterproofing has failed;
• walls in contact with damp soil.

How do you tell whether the damp is capillary?

The appearance of the wall alone does not always establish the cause.

Capillary damp is often marked by:

• damp starting at the bottom of the wall;
• a gradual transition to a drier zone higher up;
• white or whitish salt deposits;
• paint flaking and falling away;
• plaster breaking up;
• a distinct boundary between the damp and the dry part.

Similar signs can appear with other problems, though – a leak on the water supply or the drainage, water penetrating from outside, failed waterproofing or condensation.

Proper damp diagnosis is therefore the first step.

Capillary damp or a leak?

This is one of the most important questions.

If there is a concealed leak on the water supply or the drainage, drying the wall will not on its own solve the problem. The same applies where water is penetrating through a foundation, an external wall or failed waterproofing.

Before any drying is undertaken, it has to be established where the moisture is coming from and how it moves through the structure.

Where necessary, moisture measurements are taken at various places and depths, to give a more accurate picture of the state of the masonry.

Why won’t fresh plaster or paint solve it?

The first reaction to a damp wall is often:

„We will strip the old plaster, re-plaster and paint.“

That may improve the look of the wall for a time, but if the cause of the damp remains, the problem can return.

Where moisture is rising by capillary action, the new plaster is again exposed to that moisture and to the salts the masonry contains.

It matters, therefore, to establish the cause first and to choose a method after that.

Electrophysical drying of masonry

Where capillary rise of moisture has been established, there are various approaches to putting the building right.

One of them is electrophysical drying of the masonry, which uses a specialist system to act on how moisture moves through the structure.

ProKanal offers electrophysical drying of masonry with DRYMAT® SISTEME GmbH technology.

The method is intended for cases where capillary rise of moisture has been established and controlled intervention in the wetting process, and the drying that follows, is called for.

How does the process go?

The work starts with diagnosis and measurement of the moisture.

Depending on the particular property, what is assessed is:

• the degree of wetting;
• how the moisture is distributed through the wall;
• the height of the affected zone;
• the characteristics of the masonry;
• the possible causes of the damp.

Once the cause has been established, it is judged whether electrophysical drying suits the particular case.

After the process has started, the state of the masonry can be followed through subsequent measurements.

Important: every damp wall is different

There is no universal solution for a damp wall.

Before a drying method is chosen, several questions have to be answered:

• Where is the moisture coming from?
• Is it rising by capillary action?
• Is there an active leak?
• Is there a problem with the waterproofing?
• How wet is the masonry?

Only then can it be judged which approach is right.

Do not cover the damp up — find the cause

A wet wall is not merely a cosmetic problem.

If you are seeing:

• damp at the bottom of the walls;
• flaking paint;
• plaster fallen away or crumbling;
• white salts;
• persistent damp patches;
• damp in a cellar or on the ground floor,

it is not a good idea simply to cover the problem with fresh paint or plaster.

The first step is diagnosis.

ProKanal carries out damp diagnosis and offers electrophysical drying of masonry where moisture is rising by capillary action, with DRYMAT® SISTEME GmbH technology.

Read more about the building drying service