What Causes a Wet Patch on My Wall After Rain?

Discovering a wet patch on your wall after rain can be a concerning issue for any homeowner.

Not only can it spoil the appearance of your home, but it can also indicate deeper underlying problems.

If left unchecked, these wet patches can lead to structural damage, dampness, and mould growth.

But what causes this problem, and how can you identify and resolve it?

In this article, we’ll explore the root causes, signs, and solutions to help you tackle the issue effectively.

What Causes Wet Patches on Internal Walls?

Wet patches on internal walls typically occur when moisture from outside the property seeps into the walls.

This is often exacerbated by poor building maintenance, faults in the property’s structure, or environmental factors such as heavy rain.

Common causes include faulty gutters, rising damp, roof leaks, and poor waterproofing.

Understanding the source of moisture is key to resolving the issue.

Let’s look at how rain affects buildings and where moisture originates.

How Heavy Rainfall Can Affect Buildings

Heavy or consistent rainfall can expose weaknesses in a building’s structure, leading to moisture ingress.

Over time, elements such as roof tiles, external walls, and waterproofing can degrade due to constant exposure to the elements.

When this happens:

• Rainwater can penetrate porous surfaces such as brick or mortar.
• Faulty guttering or drainage systems can cause water to pool near walls.
• Water pressure can force moisture through cracks and openings.

Buildings that are older or poorly maintained are particularly susceptible to water damage during heavy rainfall.

If proper preventive measures are not taken, recurring rain can cause damp patches to worsen.

Common Sources of Moisture

Understanding the source of moisture is crucial for identifying the cause of wet patches on walls.

Common sources include:

1. External Water Penetration: Water entering through damaged roofs, walls, or windows.
2. Condensation: Moisture forming inside the home due to signs of humidity.
3. Rising Damp: Moisture travelling up from the ground through walls.
4. Leaks: Water leaking from pipes, gutters, or roofing.

Each of these sources has its own signs and solutions, which we will discuss further.

Common Reasons for Wet Patches on Walls

1. Poor Waterproofing

Poor waterproofing in a property allows rainwater to penetrate through external walls, windows, or the roof.

This is particularly common in older buildings where the waterproof membranes may have deteriorated over time.

• Signs: Dark stains, wet patches, or flaking paint.
• Solution: Apply external waterproof coatings or sealants to walls, inspect and repair cracks, and replace degraded membranes.

2. Faulty Gutters & Drainage

Gutters and downpipes are designed to channel rainwater away from your home.

However, if they become blocked or damaged, water can overflow and seep into walls.

• Signs: Wet patches on walls near ceilings or external corners.
• Solution: Regularly clean gutters and downpipes to prevent blockages. Repair any leaks or misalignments.

3. Condensation

Condensation occurs when warm, moist air inside the home comes into contact with colder surfaces, such as walls or windows.

This can create moisture that appears as damp patches.

• Signs: Wet patches with no external cause, often in poorly ventilated rooms.
• Solution: Improve ventilation by using extractor fans, dehumidifiers, or opening windows regularly.

4. Rising Damp

Rising damp occurs when moisture from the ground travels upwards through walls due to capillary action.

This usually affects lower parts of the wall and is more common in older properties.

• Signs: Tide marks, peeling paint, and salt deposits at the base of walls.
• Solution: Install or repair a damp-proof course (DPC) to prevent moisture rising through the wall.

5. Roof Leaks

A leaking roof can allow rainwater to penetrate the structure, leading to wet patches on walls or ceilings.

Damaged roof tiles, missing flashing, or poor roof maintenance are common culprits.

• Signs: Wet patches on ceilings or upper walls after rainfall.
• Solution: Inspect and repair roof damage, including tiles, flashing, and underlay.

3 Main Categories of Dampness

Understanding the three main types of damp will help you diagnose the issue correctly:

1. Penetrating Damp

Penetrating damp occurs when water enters through external walls, roofs, or windows.

It is typically caused by poor waterproofing, faulty gutters, or structural defects.

Common Signs of Penetrating Damp

• Wet patches on walls after rain.
• Dark or damp stains on external walls.
• Mould growth in isolated areas.
• Flaking paint or damaged plaster.

2. Condensation

Condensation is the most common type of damp in homes.

It is caused by poor ventilation, leading to moisture build-up from cooking, bathing, or drying clothes indoors.

Common Signs of Condensation

• Wet patches that appear in winter or in rooms with high humidity.
• Mould growth, particularly in corners and on windowsills.
• Water droplets on windows and cold surfaces.

3. Rising Damp

Rising damp is caused by moisture moving upwards from the ground through porous materials such as bricks or mortar due to capillary action.

Common Signs of Rising Damp

• Damp patches and tide marks on lower walls.
• Peeling paint or wallpaper.
• Crumbling plaster.
• White, powdery salt deposits on walls.

Does Rising Damp Cause Salt Attack in Concrete, Brick or Mortar?

Rising damp can cause salt attack, also known as efflorescence, in concrete, brick, or mortar.

As moisture travels through these materials, it dissolves salts.

When the moisture evaporates, the salts crystallise on the surface, causing damage to the material.

Signs of salt attack include:

• White, powdery deposits on walls.
• Crumbling or flaking mortar and bricks.
• Structural weakening over time.

Addressing rising damp promptly is essential to prevent salt-related damage.

Stopping Rising Damp with DPC Injections

A common and effective solution for rising damp is damp-proof course (DPC) injections.

This process involves injecting a silicone-based liquid or cream into the base of walls to form a waterproof barrier.

How it works

1. Holes are drilled into the wall at regular intervals.
2. The DPC fluid is injected, creating a horizontal barrier that prevents moisture from rising.
3. Once dry, the area is re-plastered and redecorated.

DPC injections are cost-effective and long-lasting, making them a popular choice for addressing rising damp.

Conclusion

Wet patches on walls after rain can be caused by a variety of factors, including poor waterproofing, faulty gutters, roof leaks, condensation, and rising damp.

Identifying the root cause is essential for finding an effective solution.

Regular property maintenance, such as cleaning gutters, inspecting roofs, and improving ventilation, can help prevent moisture issues.

For more severe cases, professional solutions like waterproof coatings, damp-proof courses, and DPC injections may be required.

If you notice persistent damp patches, it’s important to take action promptly by contacting a professional drainage expert like KD Pumps.

Ignoring the problem can lead to structural damage, mould growth, and expensive repairs down the line.

By understanding the causes and solutions outlined in this article, you can protect your home and keep your walls dry and comfortable year-round.