Walls can take 10 moths to dry out therefore it is important to establish is remedial actions are effective.
This is best achieved with a damp meter kept in constant contact (such as data-logger where electrical flow is measured regularly, hourly daily, weekly) or by test damp in exactly the same place. This is best achieved with a stainless steel screw or nail kept in the same place.
Use a simple damp meter costing about £10 to monitor dryness. They are not accurate when compared to each other i.e. they are not calibrated and therefore not typically accepted by a court.
However relative to its own readings, a mini damp meter will tell you if the wall is ready to redecorate.
Below 20% is considered dry, but the inside wall may still be damp, see below.
Protimeters are expensive and can be calibrated making them more persuasive, but the technology is the same as any other damp meter, a battery and volt, resistance or amp meter.
Damp meters measure electrical conductance. Water is a poor electrical conductor. It is salts in water that conduct electricity. Despite criticism, damp meters are a good test of dryness. Protimeter readings below 20WME are considered dry.
Protimeter survey aster has a radio frequency mode, where radio signals are deflected by dense matter, such as water, metal or concrete, in a similar way to mobile phone signals. Above 200 REL needs further investigation.
Protimeter datalogger log damp meter readings alongside humidity and temperature.
They are not as useful and regular, weekly logs using a damp meter.
Regular logs using a damp meter
Here a damp meter is used to monitor the dryness of a wall at different depths, using 1) surface readings, 2) copper nails (that don’t rust as quickly as steal) and 3) screws in half length raw plugs.
Be aware the measure of conductance is a function of a) salts, b) dampness, c) distance between two pins, d) the surface area of the pins. Therefore copper nails about 1cm into the wall will exaggerate the dap meter readings. However it is a good means of monitoring how a wall is drying out within the wall.
Here a two 150mm raw plugs are inserted into a wall with electrical wires to test deep within a wall after a flood.