I recently received this email from a scientist who had one of these systems installed in his home. This is his story:
I read your account of electro-osmotic damp-proofing with much interest as I have a Lectros dpc system in my house, and it has actually made things worse, not better.
It was a legacy of a previous occupant who obviously did not understand chemistry.
My story is as follows. I had a damp problem centred around the old fireplace in my dining room. About 10 years ago I called in a professional surveyor who gave excellent advice. Firstly he dismissed the electro-osmosis system saying, bluntly, "They don't work" - and mentioning he had been called as an expert witness to testify against the firm in the past and that they probably didn't like him.
He told me that underneath the thin skin of concrete in front of the fireplace was likely soil, which was acting like a wick drawing up moisture from the ground. I should smash up the concrete, dig out the soil, and put a board over the hole, and also replaster the affected areas. He was absolutely right, I did what he said and the problem almost disappeared - but not quite. One stubborn patch just above the skirting, about the span of a hand, obstinately refused to dry out. In the end I gave up waiting and painted over it. Over years the paint became discoloured, and four other, much smaller, patches appeared, each just above the skirting, and spaced along the wall around the old fireplace (it's the adjoining wall to the neighbouring property - it's a semi). I left the Lectros system in place and switched on, even though I could not see how it could work. The claims on the internet did not seem plausible.
Water is a neutral molecule. It is polar, it does have an unevenly distributed charge, the oxygen is slightly -ve, the hydrogens slightly +ve, but overall it is neutral. Being neutral it will not be attracted to, or repelled by, an electric field. So I could see no reason why it should move away or towards electrodes. But I left the wire in place anyway. Tired of the discoloured patch, and with 4 small additional ones, I decided to do something about it. Today I pulled up the carpet, removed the skirting boards, and the board over the hole. Each one of the 5 patches of damp coincides with where the wire contacts the wall. Elsewhere is dry. So, being a chemist, I starting to wonder what was going on here. I concluded that the Lectros system is electrolysing the small amount of water in the wall!
As you'll know, damp will draw up dissolved salts from the ground, or out of the mortar itself. These may leave efflorescence where the solution dries out on exposed surfaces. Being hygroscopic they may even cause damp to linger. An aqueous solution of inorganic salts will conduct electricity. The water molecules themselves will not move under influence of the electric field, but the ions will. So if you have a little sodium chloride present, the sodium cations will head for the cathode, wherever that is, while the chloride heads for the anode. As I understand it, the wire that contacts the wall is the anode. Thus, on arrival at the anode, the chloride ions will lose electrons and became chlorine gas. This reacts with water forming hypochlorous and hydrochloric acids. These in turn will react with the lime in the mortar and form their respective calcium salts. Calcium chloride is, of course, highly deliquescent - it attracts water and becomes wet!
Now I know why the damp refuses to go away, and why it is concentrated where the wire contacts the mortar. I have just done a little wet chemistry in the kitchen and confirmed that the soggy mortar and plaster are full of soluble sulphate and chloride (both of which will be drawn to the anode on account of their electric charges). There is also a soluble, colourless cation with an insoluble carbonate, probably magnesium. I suspect it is actually magnesium chloride (which is at least as deliquescent as calcium chloride) that is keeping everything moist, as the sulphate would form sparingly soluble calcium sulphate. Mg is a common minor constituent of natural lime anyway, as you well know from your geology/mineralogy knowledge. I thought I would share this with you, in view of your interest in gathering a scientific case against the electro-osmotic system. As a chemist I was never entirely convinced, but now feel I ought to have known better than to leave it on anyway.
I have unplugged it, and it will not go back on.
Now I am faced with dealing with a patch of plaster, with brick & mortar behind it, loaded with Mg chloride and sulphate. Replastering is no big deal, but I am concerned the Mg salts will just diffuse through in time and bring back the problem. Maybe there is an impermeable coating that could go over the brick, and under the plaster? Suggestions welcomed!
I have done some more research, and chemistry. Wikipedia has an entry on electro-osmosis, which brought back dim memories of being taught about electrical double layers at university about 30 years ago. I was right about water molecules being overall neutral, but what is supposed to happen is that the system exploits the double layer that forms at the water/solid interface. Positive ions in the water side of the interface (presumably protons) then drag or push water molecules along with them as they head for the cathode. So there is a physical principle behind it. Of course, whether it works in practice is a different matter, and even Lectros admit the literature is sparse.
Now back to my own situation. It was 2006 that I got the surveyor in, not ten years ago (memory must be failing). In 2007 I took photos that show concentric rings of yellow-brown discolouration, like a halo, around the points where the wire enters the mortar. Looking again today, each entry point is surrounded by a yellowish brown halo, like ferric iron staining. Some more chemistry in the kitchen has confirmed that I am dealing with chloride and sulphate salts (can't test for nitrate, but it could be there too) of Mg, with lesser NH4, Al, Ca and Fe(III). The Fe(III) will be the source of the iron staining. The ammonium is probably due to the proximity of an old fireplace (coal soot contains ammonium salts).
So now you have an example of a new problem with the electro-osmosis system. It causes electrochemical reactions at the points the wire enters the mortar. These reactions create soluble salts which, being hygroscopic, keep the area damp all the time. As fast as the osmosis drags the moisture away, it is replaced by fresh moisture absorbed from the air by those salts. And the Fe stains and discolours the wall. I can send you a jpg of concentric rings of iron staining surrounding the wire anode if you want - more proof of the poor performance of this system.
