Random Damp Spots on Your Walls? How to Identify and Fix the Issue

Random Damp Spots on Your Walls? How to Identify and Fix the Issue

10th February, 2023

Random damp spots on the walls in your home can drive you mad. Where are they coming from? What’s causing them? Is it penetrative damp, rising damp, or condensation? Maybe the damp spots on your walls keep coming back, even after you’ve painted over it. It’s a frustrating problem, that might seem to have no clear solution.

Dampness in the home, however it appears, isn’t something to ignore. It can lead to structural damage, and even cause health problems. What’s more, it can negatively impact the energy efficiency of your home, which is something we’d all like to avoid in the throes of an energy price crisis.

So, what causes damp spots on walls, how do you identify them, and what’s the solution? This guide will tell you everything you need to know.

Causes of Random Damp Spots

The most frustrating thing about random damp spots on your walls is that it’s not always obvious as to where it has come from. There are plenty of potential causes, and it’s not always easy to figure it out. If you are not sure, then here at London Damp Surveys, we can help. An independent damp survey is the best way to figure out exactly what’s behind the damp spots on the walls, and what kind of work you’ll need to be ready for if you don’t want them to return.

However, there are a few common causes to be aware of. These are:

Lightweight Plaster

Also known as gypsum plaster, lightweight plaster is easy to work with and cheap, so many tradespeople and DIY enthusiasts love it. However, since it has a lower density and water resistance in comparison with traditional sand and cement plaster, it’s more susceptible to absorbing moisture from the air, leading to – you guessed it – random damp spots on the walls.

If lightweight plaster is used in areas of the home that tend to be moister than others, such as in the bathroom or kitchen, the walls can easily absorb moisture from the air in the room, leading to damp. This is even more likely to happen if the plaster hasn’t been properly sealed or painted, as this means that it’s effectively got no damp protection at all.


Condensation is another common reason for why you’ve got random damp patches appearing on the walls. Condensation occurs when the humidity in the air encounters a cold surface, like a wall, and the vapour condensates into water droplets.

Condensation can occur anywhere in the home, as lots of the everyday activities that we do like cooking, showering, making a brew, and even breathing cause water vapour to collect in the air. However, a home may be more prone to condensation and damp problems if it does not have proper ventilation.

Vents in your home are essential for preventing condensation and damp, as they provide a colder place for the water vapour to go and evaporate outside instead. Even installing vents in high-humidity areas, like the bathroom and kitchen, can make a big difference in terms of your home’s damp risk.

A dehumidifier in your home is also a great option if you’ve noticed random damp spots on the walls and believe condensation to be the cause. These machines work to pull the moisture from the air, instead of it ending up on your wallpaper.


You should check for any leaks in your home if random damp spots on the walls have suddenly appeared. Leaks can occur in any part of the home; however, you’re more likely to get them in the roof, walls, and floors.
They can be caused by a variety of reasons, including poor construction, damage from the elements, and general wear and tear. Pipes that run through or near the walls, for example, might crack over time with age, causing leaks that show up as damp patches on the wall.

Rising Damp

It’s worth checking the location of any damp patches that are appearing on your wall. Are they located on the top, the centre, or the bottom of the wall? On the top and centre, the culprit is likely to be one of the causes mentioned above.
However, if you are noticing random damp patches appearing near the skirting boards and the bottom of the wall, you might have an even more serious problem on your hands. This is a common sign of rising damp, which is an indicator that your home’s damp proof course has failed.

The damp proof course is a waterproof treatment applied to the foundation of the home to prevent water from outside getting into the foundation and causing damp problems. When it fails, there’s no barrier present to prevent the moisture from getting in and wreaking havoc.

Whether it’s rising damp, penetrative damp, or damp caused by condensation in your home isn’t always easy to spot. That’s why we recommend a property survey carried out by one of our damp proofing London specialists. They will be able to cast an expert eye over your problem and let you know if you need to get a new damp proof course fitted, or if something else is the cause. Damp proof course replacement can be an expensive job, so home surveying is well worth it. They can also let you know if a rising damp treatment is recommended.

How to Prevent Random Damp Spots

The good news is that when you know what causes them, it’s easier to prevent random damp spots from appearing on your home. Some key preventative measures to take include:

Ventilate: Make sure that all the vents in your home, especially those in the kitchen and bathroom, are working correctly and used when necessary. If not, open windows often.

Dehumidify: If you can, invest in a dehumidifier for your home. Even a small, inexpensive one can make a difference to condensation levels.

Damp treatment: If your home has gypsum plaster, and you can’t afford to replace it, painting with a damp sealing treatment before decorating can help improve its moisture-resistance.

Inspect: Finally, keep your eye out for leaks, and keep your home well-maintained to avoid them.

Random damp spots on the walls can be a frustrating issue. If you’ve noticed them, and aren’t sure how to solve the problem, give us a call – our damp specialist London team is always happy to help.