Let painted walls breathe

house drain blocked with root growthKeeping your home’s gutters, rainwater downpipes and drains clear and in good condition is by far the best way of ensuring your home stays free of damp. Looks for evidence of dark patches, water stains or algae growth on walls which can often reveal hidden problems such as cracks.

If your property is painted, the application of the wrong type of paint to the building’s external walls can cause it to act as a waterproof barrier. This may prevent moisture entering the building from the outside but can lead to a build-up of moisture within the wall, which will make the house damp.

Moisture from within the building needs to escape. Of course, internal heating and ventilation are important, but sealing the building with an impermeable external coating will cause damp problems from our normal everyday activities, such as cooking, washing, showering and simply breathing or perspiring.

External waterproof coatings

Beware of applying an external coating to act as a waterproofer to keep it dry. It may seem logical but there is a fundamental problem with this theory: most damp within a building comes from inside the walls, not outside them.

Preventing the building from breathing and allowing outside moisture to simply run down the external walls of your home will have the effect of concentrating that moisture at ground level which can in turn flood land and drains and cause problems with the footings.

You can liken this effect to wearing a cagoule. A cagoule might keeps water away from your upper body – but it makes you sweat and soaks your legs. In a building, it is far better to spread external moisture across a larger wall area to enable it to evaporate quickly when it eventually stops raining.

Impermeable coatings can also crack, allowing water to penetrate and preventing moisture from escaping through evaporation which may cause damp patches within the building. Reversing the application of an external wall finish to the building will require extreme measures, such as stripping the render.

Internal wall coatings

DON’T use waterproof paint on the internal walls of your home! Painting an internal wall with a waterproof coating does not prevent damp problems within the building but has the effect of sealing any damp behind the barrier. Damp sealers will only cause the patch of damp to appear on another area that hasn’t been treated.

Equally, there is no point in decorating an internal wall that is showing signs of damp without first dealing with the problem. The damp will eventually bubble or peel and mould will build up causing even more damage to the property. When you found a solution, make sure you remove all signs of damp and mould before redecorating.

Other preventative measures

Check the pointing on an older building regularly to ensure its integrity. If you do need to repoint, make sure you use a suitable material, such as lime mortar, in place of Portland cement which may in time crack, pit or crumble. Lime mortar is better suited to weathering and aging as it is permeable and flexible. It is not susceptible to frost and can hold moisture without becoming ‘wet’.

Using a lime wash to paint walls is cheap and has been in practical use for four thousand years.

Rising damp

If you have damp on the ground floor of your property that is around 4ft from the floor (although it can be higher), it could well be rising damp; damp further up the wall or in upstairs room is likely to be penetrating damp, a plumbing failure or another cause.

Rising damp is the term used for the absorption of water through bricks and mortar of a building by capillary action, which causes moisture to rise. Read more about rising damp in our article.

Ask for advice from a Chartered Surveyor before comprising the future condition of your property.

Back to October 2019 Newsletter

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