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How to test for damp 1

How to test for damp

Testing for dampness using a conductivity ‘pin’ type meter is intended to allow the user to compare readings in order to interpret the pattern and deduce the likely cause(s).

Do not use the meter to justify expensive building works without consulting a qualified expert because high conductivity readings can be caused by ‘salts’, foil backed plasterboard, aluminium paints etc.


Look for these symptoms and mark them on your sketch plan;

  • water stains, discoloured paint, paper
  • white crunchy salts on the surface, or pushing off the paint or paper
  • mould, black or green
  • a tide mark, often a wavy line along the wall (note the height), at low level
  • loose crumbly plaster, or hollow when tapped with the knuckles
  • skirting board creasing, inward or outward, or splitting into cubes
  • there is plaster right down to the floor (‘bridging’ the DPC) – tap the skirtings with your knuckles, they should sound hollow at the base
  • soft, sagging, bouncy or rotting floor boards (check air bricks – size, number)
  • insect holes (measure the diameter, use a magnifier)
  • chimney breast stains (which floor, any ventilation?)
  • solid floor damp – check the wall to floor joint at the edges
  • water leaks from kitchen or bathroom fixtures or machines
  • leaking gutters, downpipes, drains
  • high external ground levels relative to DPC



  1. Use the pins lightly on the surface of the walls and note readings. Take readings in damp affected areas every 100mm up and across the wall to establish the extent of the problem.
  2. In the areas of highest readings try to push the pins further into the wall. Are these readings higher, is the plaster soft or hard, or too hard to penetrate?
  3. Take readings from an unaffected area in the same room to see how much of the reading is ‘normal’ for that building at that time of year. A steady, low background reading in an old building does not necessarily indicate a fault.


  1. Rising dampness is generally indicated by readings which start in the skirting board and continue to between 6 inches (150mm) and 20 inches (500mm) up the wall, with a sharp cut off, from high reading (say 2%) to zero over the space of 2 inches (50mm) or less.


  • Take lots of readings
  • Draw a sketch of the area
  • Note the readings
  • Look for the pattern
  • Look for visual clues
  • Check with an ‘expert’


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