How to Damp Proof

Insider’s Damp Proof Guide (top tips);

  1. Locate the source of dampness.
  2. Measure the damp.
  3. Self diagnose the cause of damp.
  4. Establish the risk of rising damp.
  5. Establish the risk of rot.
  6. Simple check for condensation.
  7. How to check if you have a leak.
  8. How to check if you have penetrating damp.
  9. See how much you just saved yourself.
  10. If you have any doubts check your findings with an expert.
Damp Proof Guide
Don’t misdiagnose call an independent expert

Locate the source of dampness.

This is the most important stage. Misdiagnosing the type of damp can cause harm, with minimal short-term benefits. For stance treating a property for rising damp, when the problem is condensation, could easily result in dry rot.

It takes years of identifying the source of ingress in damp properties to become an expert, however owners are often in a better position to accurately diagnose damp, then they think they are;

Identification, start by elimination;

  1. Is there a circular light brown stain on an external wall, normally in one, or a few isolated spots, possibly below ground level?
    1. If so you probably have an external leak or penetrating damp.
    2. Measure location, look on the other side of the wall, and slightly higher. Look for white, green or dark stains on the brick work or render. Check what happens to rain in a storm, it could be a gutter.
  2. Is there a brown stain on the ceiling, or high up on the wall.
    1. If so, you probably have an internal leak from above the ceiling or penetrating damp through the roof.  The stain comes from organic matter, maybe timbers, and typically looks like the stain left by a tea bag.
    2. Measure location, look on the other side of the wall, ceiling, loft roof. Listen for a leak, turn pipes off. Waste water can be test with blue dye or florescent.
  3. Is there a distinct horizontal line?
    1. If so, you probably have a flood, or leak on a solid floor, without a gap between the plaster and solid floor (normally the 10 – 20mm is hidden behind the skirting boards).
  4. Is the damp in patches, typically by external doorways, windows, top floor ceilings, imbedded metal (pipes, RSJs, sockets etc), unventilated bedroom or areas near bathrooms or kitchens?
    1. You probably have condensation.
  5. Do you have mould?
    1. You definitely have excess humidity, the cause of condensation (at least around the area where the mould is visible).
  6. Do you have visible surface salts on the outside or inside of the wall?
    1. If so you probably have condensation.
  7. Is the damp above a solid floor?
    1. If so you probably have condensation on the solid floor, being absorbed up the wall by the plaster (easy and cheap to fix).
  8. Is the damp patch more or less horizontal, located on the ground floor, but above ground level, and the property in a high water table area (flood risk area) check?
    1. If so you may possibly have rising damp, if you live in London (UK) we offer a money back guarantee on all rising damp surveys, ask for details.
    2. Note if the property has previously had damp treatment and the damp returns (often at the edges), then you almost certainly never had rising damp.
    3. Note that damp resulting from raised ground levels is not rising damp, it is penetrating damp and easy to fix (by putting the ground back to it’s original level).

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Measure the damp.

The most effective measuring devices are;

  1. A series of photos or video over time possibly even a time lapse overnight with the light on (do send us a copy for an expert opinion – the only stipulation is we can use those photos to further our guidance for other users).
  2. A pencil to mark the area with a date or photo of the pencil mark.
  3. A humidity meter to record temperature and humidity over the period of a day or more, record the data. The best meter record high and low temperature and humidity levels, check our guide on for dew and mould points; using the high humidity and low temperatures.
  4. A measuring tape to accurately identify what is on the opposite side of the wall (which may require a friendly work with the neighbour). Clearly, if the neighbour’s side of your damp wall is dry, then you can eliminate rising damp.
  5. A ladder and long monopole (“selfie stick”) is the modern way of checking roofs, flashing, flaunching, pointing, chimneys etc from the outside.
  6. A damp meter. The price ranges from £10 – £1,000. Most damp meters do the same things, measure electrical conductivity between two points. If you measure the distance between the damp meter pins, hammer in two non-corrosive nails into the wall, you can take accurate measurements over time. Don’t forget the low meter readings are at least as important to record as the high meter readings.

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how to identify mould
Mould caused by condensation – easy to clean

Self diagnose the cause of damp.

Essentially the self diagnosis takes place in step 1, locate the source of dampness. However, damp is often cumulative. For example you may have a leak that is causing low level flooding, with a horizontal “tide” mark, as well as mould and patches of damp around cold external walls.

So it is important to deal with the easiest form of damp first, for instance if there’s a leak, turn the tap off.

If there is condensation, open the window, improve ventilation, increase the delay on the extractor fan.

We’re happy to help, send us your photos (the only stipulation is we can use those photos to further our guidance for other users).

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Establish the risk of rising damp.

Be careful not to treat a property for the wrong cause of damp, you could either waste money, or worse, cause damage such as timber rot.

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damp cause penetrating damp
Rising damp misdiagnosed

Establish the risk of rot.

Rot requires a substantial amounts of damp, such as condensation on a cold water pipe, penetrating damp and leaks. There is insufficient moisture in rising damp to cause rot.

This is why it is so important to correctly diagnose the dampness, do not treat for rising damp if the cause is condensation. you could be risking rot, a much greater risk.

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Simple check for condensation.

The simplest check for condensation is look at the windows in the morning. If water has condensed then you have condensation.

An alternative that is particularly useful for knowing when you can close the backroom window, or turn the extractor fan off, take out an old mirror from it’s frame, stick the back of the mirror on the damp wall or window look for signs of condensation.

The modern way is use a humidity meter on the damp wall, especially one that records highest humidity levels and lowest temperature then visit our guide on for dew and mould points

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How to check if you have a leak.

Leaks take time and patience to identify. It is worth consulting you the water section of you local search, normally arranged by your solicitor during the conveyancing. The plan should accurately identify the mains water and drains.

  1. External leaks from waste pipe, gutters, hopper and downpipes are normally very easy to identify, just make sure you can see the whole of your property, look for any white, green or dark greyish streaks, observe when its wet.
  2. Mains water leak, if you have a meter, turn off all taps and appliances and record the meter reading before and after a period of half a day.
  3. External mains or drains, if the searches reveal a drain or main water pipe where you suspect a leak, then observe how well the local flora is growing and or use a listening stick, or improvise with a long metal rod. Drain water can often be smelt. Consider the fall of drains on a hill and the placement of manhole covers. Local water companies can be contacted for leak detecting, often free, even if it’s on your land. Employ a local CCTV drain company.
  4. Internal waste water (grey water), there is no  easy test, however if you can cap an end, then pour water until it backs up to the outlet, observe any significant changes in water level.

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How to check if you have penetrating damp.

There are three main types of penetrating damp, also known as water ingress.

  1. A leaking roof, valley or flashing – start by looking in the loft, check for high humidity, then feel into the cracks and crevices, use the selfie stick, damp meter.
  2. Leaking rainwater goods, should be observed during  storm, possibly filmed (best in slow-mo), and observed by looking for white, green or dark streaks.
  3. Bridging, possibly by items stacked again the wall, garden furniture than allows water to bounce onto the brickwork, flower pots, raised ground levels (possible near to or over the Damp Proof Course (“DPC”).

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See how much you just saved yourself.

Damp proofing contractors offer free surveys but the recommend expensive treatment, that may or may not be necessary, or correct and in many instances, is damaging.

Damp proofing against rising damp, condensation, penetrating damp and leaking pipes is almost always Free. The only cost is in the accurate diagnosis of the root cause. We have seen estimates as high as £36,900 for incorrectly diagnosed rising damp treatment.

Should a damp survey ever be free? The choice is;

  1. £1,000 for an expert report to identify the root cause of dampness, from a surveyor independent of any building company . Or
  2. £7,500 for a “free” estimate (sometime confusingly called a survey) from a builder’s sales person, for damaging chemical work that obscures the root cause of dampness.

Is it rising damp? Ask a Damp Proof Expert

Case study; London house; a contractor recommends treatment for Rising Damp! “Free survey” apparently. But look, contractor had already injected chemicals last time! In fact, condensation was the issue. No cost to treat, just a few vent and humidity changes.

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If you have any doubts ask a Damp Proof Expert.

If you have any doubts check your findings with an expert.

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Simon Hichens
Simon Hichens – Damp Proof Expert

Damp Surveys Ltd is an independent expert damp surveying company.  DSL was incorporated following the development of technology to accurately identify the cause of damp.

Our confidence in our equipment allows us to categorically state whether or not there is a risk of rising damp. If we are satisfied that there is minimal risk of rising damp, we can offer a warrantee subject to application and conditions.

Independence is key to understanding how we operate. And why we provide a unique service quite different to any other company.

Contractors, looking for work, offer low cost, or sometimes “free” surveys. We do not and never will benefit financially from any recommendation. We are motivated to recommend optimal treatment. To protect the property now and into the future.

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Certificated Surveyor of Dampness in Buildings
Property Care Association – Damp Proof