In this article we will analyze the electro-osmosis method to understand whether it is a definitive solution against rising damp.
Electrosmosis: what it is
Ferdinand Friedrich Reuß, at the beginning of 1800, studying electrokinetic processes, discovered that applying a potential difference to two metal electrodes, immersed in two parts of liquid separated by a diaphragm, liquid flow takes place through the capillaries of the same non-conductive porous diaphragm. This flow raises liquid level from one side of the diaphragm and depresses it on the other, stopping when the level difference reaches a value generating a liquid flow equal to and contrary to electrosmotic one.
Electrosmosis: how it works
Liquid - solid contact, which a potential is associated with, determines a double electric layer formation. The solution is not electrically neutral as it preferably contains ions of opposite sign to the solid surface charge, due to electrostatic attraction: therefore the application of an electric field moves the double layer portion not bound rigidly to the solid, thus determining liquid flow, characteristic of electrosmosis. Electrosmotic flow direction depends on the sign of the solid surface charge: if it is negatively charged, the double-layer ionic strength is positive and the liquid moves towards negative electrode.
Electrosmosis: how to install it on masonry
After making a horizontal trace on masonry, variable in height from 3 to 30 cm (depending on the type of anode), in plaster or in mortar joints at the maximum visible level reached by the humidity inside or outside the wall partition, an electric semiconductor (positive pole) will be fixed inside the trace, making either by a metal net of 250-270 mm height approx and 10 mm thick, in case it is itself conductor, or by plastic material, if current is activated by a conductive ribbon, fixed on its upper part.. In the soil near the masonry to be treated, 120-150 cm deep perforations are made, spaced 200-300 cm apart (distance strictly related to the electrical conductivity); then ferrules with negative semi conductive function, 50-65 cm long and 16-27 cm of diameter (in relation to the development of the anode) will be insert, subsequently connected together to make a ring with closed electric circuit. The two circuits will be connected in parallel, through suitable electric cables sheathed to the power supply unit which, connected to common 220 Volt power supply network, will supply the system with continuous pulsed current with values causing no corrosion of metals and plasters; voltage shall not exceed 2.8 Volts and 2m Amperes as maximum intensity per linear meter of the wall (with any masonry thickness and type).
Pros of electrosmosis
- usable on any material made with silicon
- usable on any type of masonry
Cons of electrosmosis
- metallic conductors, inside the masonry, may concentrate force lines of electric field and compromise the system
- damp masonry conducts electricity, while when it is draining, electrical resistance increases and the system tends to work in cycles
- only water portion rising by electro-osmosis is eliminated but not capillarity rising portion
- stray currents introduction can cause reinforcement bars corrosion
- completely irreversible intervention
For these considerations, professionals and technicians usually tend to recommend a solution that, in addition to acting definitively on the whole building, is also non-invasive (see KontrolDRY)