How to Treat Damp Walls Internally

If you’ve noticed damp has appeared inside your home, it’s best to get this treated sooner rather than later. If left for too long, damp can be much more problematic than just getting your walls wet. It can make your room feel cold and uncomfortable, and it can even lead to health problems and structural issues in your home. Thankfully, you don’t necessarily have to call in the pros to treat your damp walls internally. Continue reading for our advice on how to treat dampness in internal walls.

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You can determine whether you have damp in your home if you notice musty smells, cold or discoloured walls, peeling paint, mould growth, and condensation.
To treat damp walls internally, you should treat the problem at its source by drying the area first, then installing damp-proofing into the masonry. You can also apply a damp-proof membrane or paint.
To prevent damp from returning in your home, keep your space well-ventilated, use dehumidifiers, and apply anti-condensation or damp-resistant paints.

What causes damp?

There are four main causes of dampness on internal walls: condensation, penetrating damp, and rising damp. When it comes to condensation, damp environments such as a bathroom, and poor ventilation can cause moisture to build up in your home, making damp appear much quicker and in larger quantities. As long as your home is well-ventilated, condensation shouldn’t cause too much of an issue.

How do I know I have damp in my house?

If you’ve got damp in your home, there’ll be a few telltale signs:

A musty smell
Cold, damp surfaces
Discoloured brown spots
Mould spores growing on the wall or ceiling
Damp patch on the wall but no leak, or on your ceiling and the corners of the room
Flaking paint
Peeling wallpaper
Condensation on the windows

The long-term effects of untreated internal damp

Leaving damp untreated can affect both you and your home. Here’s what issues could arise:

Structural damage to your home
Mould growth
Poor indoor air quality
Long-term health issues, including allergies and respiratory problems
Reducing a property’s value
Gradually increased heating costs

Yes, damp can be dangerous as it often leads to mould which can irritate the skin, cause asthma, allergies and other respiratory issues. Also by weakening building materials, it can pose a structural risk to those living in the property.

How to treat damp with Dryrods or damp-proofing cream

Before you start exploring remedies for dampness inside walls, it’s a good idea to let them dry out. You can do this by opening all the windows and turning your heating on, or by buying or hiring a dehumidifier and leaving it to run for a while. This will take the moisture out of the air, giving the walls a chance to dry.

Before treating your damp, make sure you have the following tools and materials:

Place a dust sheet on the ground.

Once the wall has dried out, chip off the plaster that has been affected by the damp. You can do this using a chisel or bolster and a hammer, but much of the plaster may come away easily due to the damp separating it from the brickwork.

With all the plaster removed from the area, you can now start to prepare for the damp proof course installation.

Attach a long 12mm masonry drill bit to your drill.
Find out the depth of your wall and make a mark on your drill bit at about an inch shorter than this depth. This will stop you from drilling into your neighbour’s house.
Measure 150mm from the ground and find the horizontal mortar join closest to this measurement.
Drill a line of holes across this mortar line, drilling into every spot where it meets a vertical mortar line. This step is because you want the damp proofing to be able to spread through the mortar in the wall.
Vacuum any dust or debris out of the holes

If you’re using dry rods, the process is as simple as cutting them to size and slotting them into the holes you’ve drilled. These will then break down over time and spread across the mortar, creating a damp-proof barrier that’ll stop moisture from rising up through the ground.

Note: when handling dry rods, make sure to wear gloves.

If you’re using damp proof cream, attach a longer nozzle to the applicator and squeeze the cream from the back of the hole all the way to the front. This works in the same way as dry rods, eventually dispersing into the mortar across the wall.

Often, salt from rising damp will travel through the plaster and settle on your wall. For walls that are susceptible to damp, damp-resistant plaster is available to prevent this from happening, so it’s best to replaster with a product like this.

If you’d like in-depth instructions to help you tackle this process, check out our step-by-step guide on how to plaster a wall.

If you’re not comfortable doing this step yourself, call in a plasterer to finish off the wall.

How to treat damp with a damp proof membrane

Another way to treat rising or penetrating damp is by installing a damp-proof membrane. This can either come in the form of paint or a fabric membrane that needs attaching to the wall with studs or adhesive.

Here’s what you’ll need when treating damp with membrane:

Dust sheet
Damp meter
Bolster or chisel
Mallet or hammer
Tape measure
Drill
12mm masonry drill bit
Vacuum cleaner
Plaster
Plastering trowel
Damp-proof paint or damp-proof membrane
Paintbrush or roller
Mesh tape
Wall fixing plugs (may come included with membrane)
Sealant

Place a dust sheet on the ground and take off the plaster in the same way as detailed above.

Clean up any debris and prep the wall for the next step, making sure it’s completely dry.

A damp proof membrane can be attached to the wall with fixing plugs to add an extra barrier against damp. Here’s how to install it:

Cut the membrane to size, making sure it completely covers your wall. Leave some overlap for when you’ll need to join pieces together.
To join edges together, use mesh tape, pressing it down firmly to form a tight seal.
Fit the membrane to the wall with the studs facing the wall and the mesh facing outwards. Pull it tight and square as you fit it.
To secure the membrane to the wall, drill through the membrane and into the wall using a drill bit that matches the length and width of the fixing plug. Apply sealant into this hole and hammer in the plug using a mallet.

Damp proof paint can create a barrier similar to a damp proof membrane but doesn’t require making any holes in the wall. This makes it a great alternative for novice DIYers. It can be brushed, rollered, and often sprayed onto the wall for easy application.
Leave for around 6 hours to dry before moving on to the next step.

You can now replaster the wall in the same way as detailed above.

How to fix damp walls permanently

Once you’ve treated and protected the wall against damp, you’ll still want to take measures in preventing damp walls inside the house, whether it returns or it’s fresh. The best thing you can do is make sure the space is well-ventilated. Whether that means opening your windows often or investing in a dehumidifier, as both will make a huge difference. You can also use anti-condensation paint which will stop condensation from seeping into your walls and causing a larger problem.

We hope you’re confident in treating damp walls internally. If you’ve noticed damp starting to appear on your walls, it’s best to tackle it at the source rather than just cleaning it away or painting over the area. The best way to do this is by installing damp proofing which can come in the form of a cream and rods that are inserted into your masonry, or paint and a fabric membrane that can be installed onto your wall. These form a barrier to stop rising damp and condensation from soaking your walls and causing further issues. And they’re even DIY friendly! If you’re dealing with a bigger problem and the damp on your walls is resulting in mould growth, check out our guide on the best anti-mould paint.

FAQs

To dry out a damp wall, open your windows to let air circulate and give the moisture a chance to escape. To dry the wall out quicker, switch your heating on to speed up evaporation. For more serious damp, it’s wise to invest in a dehumidifier which will take moisture out of the air, so it doesn’t end up on your walls.

If your plaster is showing signs of damp, it’ll need to be removed. This is not only because it will be damaged, but also because you’ll need to get behind it to treat the problem.

You should opt for moisture-tolerant and breathable insulation for your damp walls, which includes cork insulation, mineral wool, wood-fibre boards and specialist vapour-open systems. You should always avoid foil-faced boards as these do the opposite and trap moisture, worsening the problem.

No, painting only helps from a visual perspective, but once mould begins to grow, this’ll likely penetrate the paint, making it a more visible problem. It’s best you undergo a damp wall treatment first and then apply an anti-mould paint to protect against future dampness.