Photographing damp
How to photograph a damp wall
Most damp can be identified from photographs without anyone attending — but only from the right photographs. Almost every enquiry arrives with a close-up of a stain, which is the least informative shot it is possible to take.
The three that matter
- The whole wall.Stand back far enough to get the floor, the ceiling and both ends in frame. The top edge of the damp is the most diagnostic thing in this entire subject — a fairly level line under about 1.5 m suggests rise, a blotchy edge with no line suggests condensation, and damp that is worse higher up is falling, not rising. None of that is visible up close.
- The damp, close up.Close enough to see whether there is a loose white bloom, a hard crust, black speckles, or mortar going to sand. Put a coin next to it for scale. A loose bloom that brushes off dry and a hard crust that does not are different problems with different causes.
- Outside, at the base of that wall.The garden bed, the paving, the downpipe, the ground level against the brickwork. Almost nobody sends this one, and it is frequently the photograph that answers the whole question.
Things that make a photograph far more useful
- Shoot in daylight, straight on rather than at an angle, and without flash — flash flattens the texture that distinguishes a surface bloom from a fretting face.
- Include something of known height in the wide shot. A power point, a skirting board or a course of bricks makes the height of the damp measurable afterwards.
- Photograph the same spot dry and again a day or two after heavy rain. Damp that tracks rainfall and damp that does not have different causes, and two photographs settle it.
- Mark the top edge of the damp with a pencil line and write the date beside it. How that line moves over a few weeks is worth more than any single reading.
- If there is already a quote, photograph or attach it. What a quote does and does not say about ground levels, drainage and ruled-out causes is the fastest way to judge it — see reading a damp quote.
What photographs cannot settle
Whether the moisture in a wall is free capillary water or moisture held by hygroscopic salt looks identical in a photograph, and it is the difference between a damp course and a desalination scope. So does a concealed plumbing leak. Where the answer has to hold up to somebody else, that is a drilled-sample laboratory question, covered under what an inspection can prove.
Questions about photographing damp
- How many photos does it take to identify damp?
- Three, in most cases: the whole wall from a distance, a close-up of the damp and any deposit, and the ground outside at the base of that wall. The wide shot carries the most information, because the height and shape of the top edge is the single most diagnostic feature in this subject and it is invisible in a close-up.
- Should the wall be wet or dry when photographed?
- Both, if possible. A salt deposit photographed wet looks like a stain and photographed dry looks like a bloom, and the difference between efflorescence and a lime run is far easier to see dry. Photographing the same spot a few days after rain and again in a dry week also shows whether the damp tracks rainfall, which separates falling damp from rising damp.
- Why does the outside photo matter so much?
- Because the most common causes are outside. Ground level against the damp-proof course, a garden bed built up over it, paving with no fall, a downpipe discharging at the footing, an air-conditioner condensate line — none of these are visible from inside, and between them they account for a very large share of what gets diagnosed as rising damp.
- Does a photograph of a moisture meter reading help?
- Very little on its own. A two-pin resistance meter measures electrical conductivity, and soluble salt in a wall raises conductivity whether the wall is wet or bone dry. A high reading photographed next to a skirting board proves almost nothing. A photograph of where the reading was taken, and how high up the wall, is more useful than the number.
- What should be included for scale?
- A coin, a tape or a ruler against the deposit in the close-up shot, and something of known height in the wide shot — a power point, a skirting board, a standard brick course. Height above ground level is what separates rising damp from the things that imitate it, so anything that makes height measurable from the photograph is worth including.