How to deal with penetrating damp

How to deal with penetrating damp

Credit where it’s due, water is a persistent player and relentless in its determination to invade your home through the smallest of cracks or joints. Once it’s made its way in you’re left with the unenviable task of first locating its entry point (or points), then embarking on a programme of treatment involving remedial work, good ventilation, heat and maintenance.

Dealing with penetrating damp

  • Buy an electronic moisture meter to check damp readings particularly near windows and corners of walls
  • Prevention is always better than cure so be vigilant!
  • A stale, musty smell usually means poor ventilation and consequently damp

There are three main causes of dampness: rising damp, condensation and penetrating damp. This article looks at the latter: the causes, the signs, the damage limitation and the preventative measures.

Scroll down for advice or jump to the following sections:

What is penetrating damp?

Penetrating damp is classed as any water that finds its way inside from the outside. It occurs at all levels of the building but is more prevalent higher up and on south west facing walls. Overflowing gutters, missing roof tiles, downspouts, leaking pipes, badly fitting windows or doors and damaged pointing, cladding, flashing or render are all sources of penetrating damp.

If air bricks are covered that too can cause problems because it prevents the building “breathing” by restricting the flow of air and trapping moisture which in turn leads to damp.

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What are the symptoms of penetrating damp?

You’d think it would be fairly easy to locate the ingress of water into your property but the problem is that it can often be weeks or months before any problems appear. Typical signs of penetrating damp are:

  • growing circles of damp on walls or ceilings
  • blotchy patches on walls
  • wet and crumbly plaster
  • signs of spores or mildew
  • drips and puddles.

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How is penetrating damp treated?

The key thing is eliminating the moisture at source. Alas it’s not as easy as it sounds. While a leaking gutter may be easy to repair, a damp-ridden cellar surrounded by a wet and high external ground level is much trickier. Here we look at the main treatment options available:

Reseal Take a good look at your window and exterior door frames throughout your house. Seen better days? Strip out all the old sealant and replace with a good quality silicone sealant which sticks and expands better than its cheaper counterparts.

Repoint crumbling or missing mortar between bricks. Patch repointing is fairly easy to do yourself but note that your new mortar will show up startlingly against the old so you may want to consider having a section or full wall done. Large scale repointing involves working at height with power tools so it’s a job best left to the pros.

Seal the wall Spray three coats with a proprietary water sealer. These work by soaking into the first few millimetres of brick, blocking the tiny holes and preventing water coming in. Make sure you use a vapour permeable product to allow any water vapour within the structure to escape. Please note, these products will not seal cracks.

Check cavity walls. Where no obvious cause is visible, there could be an obstruction or debris in your cavity wall which is “bridging” dampness from the outer skin of the property to the inner skin. This is definitely a job for the pros who will check the cavity using a suitable camera.

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How much expense will it take to fix?

Because damp penetration covers such a broad range of cause and effect, it’s tricky to estimate costs. Below are a range of prices you’re likely to be quoted for specific problems:

  • DIY resealing one window £10
  • Tanking an average-sized basement £1,000-£1,250
  • Repointing a 1930s semi £3,500+

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Ventilate, ventilate, ventilate

Once you’ve eliminated the source of the moisture you now need to dry it out. Buy or hire a dehumidifier to zap the moisture, keep heating on low to create a warm atmosphere and open windows and doors frequently to prevent condensation forming.

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How do I prevent penetrating damp?

  • Be vigilant. Check seals, connections and waste pipes on domestic appliances regularly. Always be on the lookout for problems (particularly if you live in an upstairs flat – think of your downstairs neighbour!).
  • Regularly check your loft for signs for water coming through the roof.
  • Check your exterior walls for decay, crumbling or cracks.
  • Keep areas around damp-proof courses and bricks clear.
  • Do not place planters directly against external walls.
  • If replacing driveways or paving do not raise the levels as you may bridge the damp proof course.
  • Twice a year check moisture levels with an electronic moisture meter.

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