Damp on external walls is more than just an eyesore—it can lead to serious damage if left untreated. Whether you’ve noticed damp patches, peeling paint, or mould growing on your brickwork– then, the first thing to do is to understand the root cause of this issue.
If you’re considering renting a dehumidifier to help with damp– this guide will help you know everything about signs of damp on external walls, its causes, and how to tackle it.
So, let’s begin..
What is an External Wall Damp?
It actually occurs when moisture seeps into the walls of a property, either through faulty masonry, damaged gutters, or rising damp from the ground. It is often called “penetrating damp”. Unlike internal damp, which is often caused by condensation, external damp usually originates outside and works its way in.
So, where is the problem if it is left untreated?- Well, it can cause mould, weaken the structure of your home, and make your living space feel cold and unwelcoming.
Having known that– you need to check for damp signs as soon as possible. Here is how..
How to Check for Damp When Viewing a House?
If you’re in the market for a new home, checking for damp is needed to avoid unexpected repairs later.
Here are simple steps on how to identify potential damp issues:
- Look for visible common signs of Damp on External Walls like– Check for damp patches (Often brown or dark marks appearing on exterior walls), peeling wallpaper (Moisture trapped under layers of paint causing bubbling or flaking), or discoloured walls, especially near skirting boards and ceilings.
- Check for a Musty Smell – Damp often has a distinctive earthy, musty odour. Pay attention when entering rooms or opening cupboards.
- Touch the Walls – Walls that feel cold and damp to the touch could indicate underlying moisture problems.
- Inspect Window Frames and Sills – Condensation build-up on windows and mould growth( green or black patches forming on the surface) on sills suggest high humidity levels.
- Examine External Walls – Look for mould, crumbling mortar, or white salt deposits (powdery residue forming due to moisture evaporation), which are signs of moisture ingress.
- Ask About the Property’s Damp History – Sellers and estate agents should disclose past damp issues or treatments carried out.
Recognising these symptoms early on allows you to take action before the issue becomes more severe.
But what causes such an issue in the first place?
Causes of Damp on External Walls
Actually, it results from various issues. Here are the most common:
1. Penetrating Damp
This occurs when water seeps through external walls due to damaged brickwork, cracked render, or faulty drainage. Common culprits include:
- Leaking gutters and downpipes
- Damaged roof tiles
- Cracks in external walls or render
- Poorly sealed windows and doors
2. Rising Damp
Rising damp happens when moisture from the ground travels up the walls due to a failed or missing damp proof course (DPC). Signs of rising damp include:
- Tide marks on external and internal walls
- White salt deposits on brickwork
- Peeling plaster inside the property
3. Condensation Issues
While less common externally, condensation can still contribute to damp problems if warm indoor air meets cold walls, particularly in poorly insulated properties.
Now-it’s time to have a look on our simple step-by-step guide to help you treat external wall damp-
Step-by-Step Guide to Treating External Wall Damp
Step 1: Identify the Cause
Before treating damp, it’s important to pinpoint the source. Where is it coming from? Is it leaking gutters? A cracked wall? Or rising damp from the ground?
Why is this important? because each cause requires a different solution.
Step 2: Repair the Damage
After identifying the cause-let’s resolve it:
- Fix any leaks – Clear blocked gutters, repair broken pipes, and check for roof leaks.
- Repoint brickwork – Replace crumbling mortar to prevent further water ingress.
- Seal cracks – Use waterproof masonry filler to close up cracks and gaps.
Step 3: Apply Waterproof Treatments
- Use water repellent coatings – A high-quality masonry waterproofer will protect brickwork while allowing it to breathe.
- Install a new damp proof course – If rising damp is the problem, injecting a chemical DPC can stop moisture from travelling upwards.
Step 4: Improve Drainage & Ventilation
- Ensure downpipes direct water away from your home.
- Improve external drainage if water pools near your walls.
- Inside, use dehumidifiers to control moisture levels and prevent further damp problems.
How Can a Dehumidifier Help?
A dehumidifier won’t fix external wall damp at its source, but it can hugely reduce excess moisture inside your home. But what if damp has already made its way to internal walls? Then a dehumidifier will help by:
- Removing moisture from the air
- Preventing mould growth
- Speeding up drying times after repairs
For short-term relief or while waiting for repairs, renting a dehumidifier can make a huge difference in managing the issue.
We offer several products to help reduce moisture inside your place.
For instance, Condensing Dryer K3 HP B has two fan speeds, which makes the machine very adaptable. The machine is robust, stackable, compact and ergonomically designed, which facilitates the work and makes it easy to move between dehumidifying assignments.
It is extremely quiet, which is a great advantage when used in residential environments.
To explore more; Check our range of products here
FAQs-Signs of Damp on External Walls
How do I know if I have external damp or condensation?
External damp usually appears as stains or moss on brickwork, while condensation tends to cause water droplets on windows and internal walls.
Can I paint over damp patches on exterior walls?
No, painting over damp walls without fixing the cause will only mask the issue temporarily. The damp will continue spreading beneath the paint, leading to peeling and damage.
How do I prevent damp from returning?
Regular home maintenance is key—keep gutters clear, fix cracks in walls promptly, and apply waterproofing treatments to exposed brickwork.
Do I need a professional to fix external wall damp?
For minor issues, DIY solutions like repointing and sealing cracks may be enough. However, for persistent or severe damp problems, a professional damp survey is recommended.