Insane in the damp-proof membrane!

There’s a reason that “moist” is the most hated word in the English language and it’s not the reason you think, potty-minds.

Period properties are more at risk from damp-related issues than any other type of building and clay-bound London has the largest number of period homes of any European city.

Is it any wonder that here at Gareth James we find both buyers and sellers, landlords and tenants affected by issues arising from rising damp, penetrating damp and condensation (the 3 most common types of residential moistness)?

Each needs to be treated in differently and damp repair costs can vary dramatically, so it's important to know what type of damp is affecting your home and how to combat it. Let’s start with the most common type….



Unless the moist air can escape through an open window, air vent or extractor fan, it'll be lurking about until it finds a cold spot to condense leading to mould forming in corners, windows, wardrobes and cupboards, paint and plaster damage and that unpleasant smell you thought was your partner’s socks / dog’s breath / partner’s breath (delete as applicable).



How to beat it?

  • Keep rooms and walls warm

Leave the heating on a low setting or set your timer switch to turn on in the morning evening for at least seven hours each day.

  • Reduce moisture

Cover cooking pots/pans, don’t leave kettles boiling, dry washing outdoors or in the bathroom with the door closed. We know this is hard for Londoners but – deep breaths – do not dry washing on radiators! Wipe condensation on windows and dry surfaces where moisture forms. Run cold water in the bath before adding hot water as this reduces the risk of steam being created.

  • Ventilate your home

Use that extractor fan, leave windows open for 30 mins after bathing/cooking, never block ventilators, i.e.vents to windows, airbricks to walls and chimney breasts! Closing kitchen/bathroom doors will stop moisture reaching bedrooms, which are often colder and more likely to get mouldy. Where possible, position furniture against internal walls and avoid placing furniture or heavy curtains in front of radiators.

  •  If you do find mould...

Wipe walls and window frames with a fungicidal wash (make sure it has a Health & Safety Executive ‘approval number’). Dry clean mildewed clothes and shampoo carpets. Do not brush or vacuum mould as this can increase the risk of respiratory problems. Redecorate using fungicidal paint (and eliminate the damp source else it'll just come back!)


 Rising damp

Rising damp is caused by ground water moving up through a wall or floor. Most walls and floors allow some water in, but it’s usually stopped from causing damage by a barrier, a damp-proof course or damp-proof membrane. When there's a lack of drainage or the level of the ground outside your home is higher than your damp-proof course, you get damaged skirting boards and plaster, peeling paint and wallpaper, that weird white, powder-like substance and tide marks along walls. Not very Living Etc.


How to beat it?

  • Repair or insert a damp-proof course

A damp-proof course is a horizontal strip of plastic or bitumen felt, built into the wall at the height of at least 15cm above ground level. Or a builder or damp specialist can drill holes in your wall and inject damp-proof cream to act as a course.  Alternative non-chemical solutions include cutting grooves into the brickwork.

  • Repair or add a damp-course membrane

A damp-proof membrane is a sheet of material, impervious to water, laid under the concrete floor and connected to the damp-proof course so that the house is sealed from ground water. Paint over a small patch of floor damp with two coats of bitumen latex waterproof emulsion. For extra protection, lay reflective foil building paper (foil-side up) as well before it's totally dried. If the damp is extensive, you may need to have the damp-proof membrane entirely replaced. This is likely to be costly, but may be necessary if the damp is widespread or other solutions haven't worked.

  • Dig away soil to level of damp-proof course

If your damp-proof course is good, the problem could be the ground level outside being built too near the top of the damp-proof course. This can be solved by digging away any soil on the exterior side of the damp wall to below the level of the damp-proof course. You could do this yourself or you could get a professional to do it.

  • Tank walls and floors in damp-proof materials

Tanking a wall or floor means sealing it to protect it from moisture by coating it (under the plaster for a wall or under the concrete for a floor) in asphalt or a membrane. Wallet alert: tanking can be very expensive so it's worth getting a few opinions to help you decide whether it really is necessary.


Penetrating damp

Penetrating damp is usually caused by structural problems like faulty guttering, roofing or cracks which mean walls or roofs are regularly soaked with water. But internal leaks, such as pipes under the sink or bath, might also be the reason for those unappealing damp patches on walls or ceilings. But there is good news, people. This type of damp can often be fixed cheaply and by yourself.


How to beat it?

  • Add a damp-proof cavity tray

Modern homes have a cavity between two walls, so moisture penetrating through the exterior wall can evaporate before it gets to the inner wall. Windows or pipework can “interrupt” this and then you’ll need a cavity tray to drain any water away from the inner wall to the outside through 'weep' holes (holes in a part of the outer wall). 

  • Replace or paint old bricks

Old bricks are porous and let water in. Get new ones or paint with an exterior silicone water-repellent fluid or limewash, that let walls breathe. This could also be a good preventative measure, too, but seek professional advice first!

  • Unblock your cavity

Forget your chakra, your cavity might be blocked and causing damp. Often it can be filled with objects, like broken mortar or brick, which take in moisture from the outer wall and pass it to the inner wall. In this case, debris will need to be cleared out to stop the issue .

We hope we've gone some way to helping you navigate the minefield that is the bane of most Londoners' lives. Unsurprisingly, Which? has a wealth of information on dampness which you can explore here


For any other mould, mildew or moistness questions, please 

Call 0207 732 4330

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Posted:11/14/18 Insane in the damp-proof membrane! Tags: damp moist fungus mould condensation rising damp penetrating damp membrane course | By Zohra Huda
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