Why do walls soak up water & cause mould when it rains?

look at the state of this retaining wall

When it rains against the walls of your home, does the water quickly disappear? If so, should you be concerned?

That water soaking into your house is because your walls are porous, they let in water, and this could be doing more damage to your property than you may think. In fact your walls at present are like a sponge, which can’t be good can it?

Jokes about SpongeBob Squarepants aside (!), the walls of your house have far more in common with your everyday sponge than you might think!

The external walls of all buildings are by far the most important part of the structure.

The roof of course has to be THE most important part of a house because if there was not a roof on the house, the occupants would get very wet!

Why does your home soak up water and what can you do about it?

The challenge that most house builders have is how to protect the structure of a building from damage, either by the sun, the snow, the wind or the rain.

A big problem with dwellings of all types in northern Europe is the fact that the outside of the property has to be kept in good condition at all times to maintain its integrity.

In the current recession (at the tim eof writing), the average person cannot generally afford to spend what little money they have, on essential tasks such as repairs and, occasionally, painting and rendering the exterior walls.

The weather attacks houses all year round.

The walls of houses generally come under constant pressure from the elements and they are built in a certain way to repel them, however over time this resistance to the weather is degraded and problems start to appear which usually require some form of expense.

The walls of a house, even if they have something like paint, render or exterior pebbledash, are buffeted by winds and soaked by the heavy rains at certain points in the year, and even the summer, with the hot sun, can bring its own problems.

The effects of the weather against the walls of houses

When cold weather arrives with the addition of the typical British rain, if houses do not have a good “sound” covering of render and/or a protective wall coating, then the rain water will soak into the house walls and cause more problems.

It is worth noting that normal masonry paint won’t truly give the house the protection that it needs.
This is a process that is very similar to a sponge.

A normal sponge that is used in the bath or shower has billions of tiny holes, and they of course soak up the water we use for washing.

If the external walls of a house are not generally in good condition and/or freshly painted, the wall itself will soak up water, via billions of tiny holes, and this is called osmosis.

The water will stay inside the walls, waiting for the temperature to plummet towards zero, and when it does, the moisture trapped inside the wall will freeze.

This is the same as when water is put into something like the ice cube tray in a freezer, and after it has frozen, the water expands and that is what happens in walls that need rendering repairs.

This is because as the water expands, the render or pebbledash gets “pushed away” from the bricks and that enables more water to come in, and then ultimately damp will occur in the house

A damp house will need urgent repair, or it will get worse.

If damp starts to penetrate through a render coating and inside a house, black mould spots and wet patches can appear inside the rooms.

The mould spots are often black or green, but the dangerous part is the fact that they release spores into the atmosphere inside the house, and although they cannot be seen, the spores are inhaled by the occupants and become stuck in the lining of the throat and lungs.

In bad cases, a house with mould on the walls can cause breathing problems and disease.

The solution to damp and wet walls?

Most surveyors will suggest that if you have damp in the house you should call a rendering contractor or an exterior wall coating company, and there are loads in the UK who can help with this problem of mould.

mold and damp on a house wall and floor

Typically their work involves identifying the source of the water ingress, curing it, and then repairing or replacing the external render or pebbledash coating.

Render must not be left bare though, because it needs extra protection to stop it cracking again, and causing mould to re-appear, so the application of a spray applied external wall coating, or a waterproof render, would be the best approach, giving a weatherproof finish that in most cases, require little or no maintenance for a very long time.

It is not normal for a house to soak up water when it rains onto the walls.

In some cases, a tiny amount of water soaked into the brick, will quickly evaporate, but a badly maintained exterior wall will let a lot of water in, too much to evaporate, and with it being water, it will find somewhere to go, usually into the house.

This means that black mould can appear on the walls, along with a quite foul musty smell.

It also goes without saying that exterior house painting on its own will NOT cure damp as masonry paint is merely coloured water! However a damp proof exterior wall coating from NPA, actually WILL cure damp ingress, plus your home will look much nicer too!

Forget DIY damp proofing, our masonry coatings are used by some of the major UK construction companies to keep damp away from theie new homes.

If this sounds like your home, please give us a call on 0800 970 4928 and let’s see if we can help you.

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