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How to repair a damaged wall

Our expert guide to fixing mouldy walls, crumbling plaster and blistering paint - plus, advice on preventing any future damage

Spray bottle and sponge near black mould wall. House cleaning concept

Whether you’re a homeowner or a renter, damaged walls are something that can affect any home. There are a number of issues that can occur and being able to spot the warning signs is the first step in dealing with damaged walls.

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We take a look at three of the most common types of wall damage – mould, crumbling plaster and blistering paint – and show you how to identify them, as well as the best methods for repair and prevention.

Mouldy walls – treatment and prevention

Why is there mould on my walls?

Mould is the result of a fungal infection, caused when warm, moist air comes into contact with a cooler surface – the moisture condenses, often resulting in black mould. It has a black or green colour – in comparison to mildew, which is usually white, grey or yellow – and looks slimy or sometimes fuzzy.

Mould can be a serious issue as, if left untreated, can release toxins into the air, which could impact your health. Unfortunately, mould spreads like wildfire; one spore can reproduce into millions of spores within just a few days.

How do I get rid of mould on a wall?

While you’ll often hear of people using bleach to treat the mould on their walls, this isn’t an effective way of dealing with the issue, as it simply wipes it away from the surface instead of killing it.

A better method is to use a fungicidal mould wash treatment. Make sure you wear appropriate safety gear, then prepare the surfaces by using a bristle brush to remove any loose material before washing down the area with the diluted mould wash and a sponge, then leaving to dry.

How can I stop mould coming back?

The best way to stop mould from coming back is to discover what caused it in the first place. The most common reason is usually down to poor ventilation. There are a number of ways to help prevent this, for example not drying clothes indoors on radiators; using an extractor fan when cooking with pans; setting your thermostat at a constant temperature to avoid extreme variations; installing a ventilation system in your bathroom.

Crumbling wall plaster – treatment and prevention

Why is my plaster crumbling?

Damaged plaster is likely the result of external issues, such as damp or impact, which, over time, can cause the plaster to become detached from the wall beneath.

In certain circumstances, timber laths are fixed between joists with the plaster pushed in the gaps between. If the laths start to rot, this can result in sagging or bowing plaster.

The warning signs of damaged plaster include cracks and bulges, loose plaster, sagging ceilings, stained patches and plaster that sounds hollow when it’s tapped. You might first notice a fine white powder on the surface of the plaster, which is caused when soluble salts move to the surface.

How do I fix crumbling plaster?

There are number of fixes you can do yourself. Any cracks and pockmarks can be filled in with matching filler. Begin by raking any loose plaster from the crack or hole with the corner of a filling knife. Then, using a small paintbrush, dampen the crack with water to make the filler dry slowly – this will help to stop it from shrinking and coming loose. Next, scoop some filler onto the filling knife and smooth it across the damage at right angles to the crack. Press firmly until the filler comes just over the surface. Leave this to dry, then smooth it down.

To patch repair plasterwork, gently treat the exposed edges of the existing plaster with water or diluted PVA – one part to 10 of water – to control suction and prevent cracking.

How do I prevent wall plaster from crumbling?

Moisture is the single greatest cause of plaster crumbling in the home, so the best prevention is to stop the damp from entering the house in the first place. This is, of course, easier said than done, but having double-glazed windows fitted, keeping the temperature regulated and even having a damp-proof course – which provides a waterrepellent barrier to your home – will all help

Blistering paint – treatment and prevention

What causes paint blisters?

Blistering is when bubbles form on the exterior paint film. This is usually caused by moisture in the underlying layer or poorly prepared substrate – a contaminated surface beneath a new paint film and solvents – which can become trapped beneath the paint film during application.

How can I fix paint blisters?

For a quick fix, use a paint scraper to remove the blister, sand the area, clean and use a joint compound to make smooth. You can then paint over it.

Debbie Hall, store manager at Leyland SDM London Bridge, has an unusual hack for fixing paint bubbles. ‘A little tip which sometimes works before reaching for the scraper – as crazy as it sounds – is to use a normal household iron to try and flatten the bubbles,’ she says.

‘Hold the hot iron against the wall for around 30 seconds. A damp seal or a stain blocker should then be applied. Tempting as it is to skip this step, doing so could lead to ugly stains seeping through the emulsion. Once complete, the area can be repainted with the same paint as used elsewhere in the room.’

How can I prevent paint blisters?

Blistering is an indication that the adhesion of the paint film is failing, therefore simply repairing the blisters is unlikely to cure the problem.

The best solution is prevention from the prep you do beforehand. Old painted surfaces need preparation, such as an adhesion test to determine the condition of the paintwork. Often, the old paint will need to be stripped back to a sound substrate before you start on any new painting.

How to fill in wall holes

Firstly, remove any nails, wall plugs or screws that might still be stuck inside the hole. Once these have been removed open the hole out using a snap or chisel knife. This will allow the filler bind to a surface. Clean away loose dust with a brush.

Apply some filler with a filling knife. Add the filler into the hole using the knife’s curved blade. If the hole is very wide or deep you might have to build up several layers. Follow the filler package instructions. It is often necessary to add a layer of filler in 10mm-deep sections and then leave it to cure before adding the next layer.

If you have a wide or deep hole to repair as detailed above, use a chisel knife to scrape away any loose plaster and neaten the edges of the hole. Dilute some PVA glue in water and apply to the hole. This will seep into the plaster and make it more solid for filling.

When the filler has cured, use some sandpaper and a cork block to sand the filler down till smooth. Then remove any dust with a microfibre cloth. You can now paint over, and the hole will be gone forever!

How to fix wall cracks

Open the crack out with a snap or chisel knife so the filler will have a surface to bind to. Use a brush to clean away loose dust.

There is some debate over the next step. For small cracks in good plaster (plaster that is not falling apart) you can skip this stage. However, for larger cracks or cracks where the plaster has been crumbling, dilute some PVA glue in water, then paint the solution into the crack with a brush. The PVA seeps into the plaster making it more solid and more reliable when adding the filler in the next step.

Apply some filler with a filling knife. Add the filler into the crack by working the blade along the length of the crack. Scrape off excess by wetting the filling knife blade and scraping from the centre to edge along the length of the crack. Check the filler packet instructions and leave to completely set and cure.

When the filler has cured, use some sandpaper and a cork block to sand the filler down until smooth. Clean the surface with a microfibre cloth to make sure there is no dust remaining. You are now ready to paint.

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Feature Colette Earley Photos Earthborn Paints; Getty Images