THE PHENOMENON


Rising damp problems are diagnosed in every part of the world. Rising damp is relatively easy to prevent and extremely difficult to treat.

Rising damp is the upwards slow movement of moisture, through porous building materials, induced by capillary absorption.

The moisture evaporates on both faces of walls or facades and usually leaves soluble salts on their surface.


These salts derive from both the soil and the building materials. They could be sulphates, chlorides, nitrates etc. and they are usually hydroscopic.

The whitish flour-like or crystalline deposits are called efflorescence (word derives from latin flora = flower). They usually form a tide-like stain on the walls.


How high can rising damp reach?


Usually the limit is about 1,5m above ground level. The height depends on:

- the capillary network of the material

- existence of hydrostatic pressure

- evaporation rate of rising moisture.


If salts reach the surface, the problem is mostly aesthetical. Sometimes salts stay behind the surface, crystallize and exert tremendous pressures to the building materials causing spalling phenomena.


DIAGNOSIS


An expert should always be advised. Many times condensation or moisture seepage are misdiagnosed as rising damp. A lot of money are thrown out of the window due to wrong diagnoses.


PREVENTIVE MEASURES AGAINST RISING DAMP


1. Better management of surface waters. Rainwater should be carried away through a properly coordinated system of gutters, downspouts and ground slopes.


2. Better management of subsurface waters with a perimeter drainage or a system of French drains (please check relevant entries).


3. Rising damp barriers under foundations based on a combination of waterproof membranes and layers of gravel.


4. Use of damp proof courses at walls bases. Usually these DPCs are made from embossed LDPE or PVC stripes.


5. Use of integral waterproofers in all below ground cement mixes.



ABOUT TREATMENT OPTIONS


1. Insertion of a new mechanical DPC by undersetting. This is the safest but most obtrusive and costly method.


2. Chemical DPCs: There are so many formulae that is very difficult to keep up pace with. Chemical treatments are more and more used during last 1-2 decades. By injecting various water repellent compounds the engineer tries to create a chemical barrier to intercept rising damp. This method is less obtrusive than mechanical DPCs but I believe less reliable too.

I 've seen many failures in the greek market and I know it's the same all around Europe. It's difficult to ensure entire wall section coverage. It's almost impossible to treat natural stone walls!

Both methods will leave behind salts above the new DPC. These salts need to be dealed with.


3. Sacrificial treatments. These are specially formulated macroporous plasters able to mask every salt attack. They need constant watch and maintenance and can create most unpleasing aesthetical effects.



Chris Strogilis