Salt Tests for Rising Damp 

 Water, which originates in the ground and rises vertically in a wall usually contains salts: Chlorides and Nitrates. If these salts are not present then it's unlikely that any moisture contained within that wall is from an external ground source, i.e. it won't be rising dampness and it's more likely to be condensation or perhaps a plumbing leak.

In a wall, these salts are left behind when the water evaporates into the atmosphere and there is usually a greater concentration of them at the uppermost point of the dampness. Consequently, if you take a sample of the plaster from this point you can test it for the presence of these salts and get a good indication of the problem.

If you have a dampness problem and you would like to rule out ground water as a source, then take a sample of the plaster sufficient to fill approximately one half of a 35mm film container or, if it's been on for a minimum of four years, remove a piece of wallpaper approximately 50mm square, and send it to me, along with a cheque for £17.50, and I'll test the sample for you.

The sampling is normally done the day of receipt and, if you have e-mail or provide a telephone number, the results can be with you the same day. Otherwise, you'll have the results within two to three working days.

The sampling is done with the Protimeter Salt Sampling Kit, which is a recognised testing agent for both Chlorides and Nitrates.