You've noticed a damp patch on your wall. Maybe it appeared suddenly, or perhaps it's been slowly growing. Either way, you need to know what's causing it—because the solution depends entirely on the source.

The Three Main Causes of Damp Walls

Damp patches on interior walls typically come from one of three sources:

1. Hidden Water Leaks

A leaking pipe inside the wall or in the floor above is one of the most common causes—and one of the most damaging if left unaddressed. Signs that point to a leak include:

The damp patch is growing or spreading
The patch is near a bathroom, kitchen, or water heater
Your water bill has increased
The damp appears suddenly rather than seasonally
You can sometimes hear water running in the wall

2. Condensation

Condensation occurs when warm, moist air meets a cold surface. In Lanzarote, this is less common than in colder climates, but it still happens—especially on north-facing walls or in rooms with poor ventilation. Signs of condensation:

Damp appears in winter and improves in summer
Black mould is present (common with condensation)
The damp is in corners or behind furniture
Multiple walls or windows are affected
The room feels humid or stuffy

3. Penetrating Damp

Water entering from outside—through cracks in walls, failed waterproofing, or gaps around windows—is called penetrating damp. Signs include:

Damp appears after rain
The damp patch is on an external wall
There are visible cracks or damage on the outside
The damp is near windows, doors, or roof level

Why Finding the Source Matters

Here's the problem: the damp patch you see on the wall is rarely where the problem actually is. Water travels—it runs along pipes, tracks across ceilings, and follows the path of least resistance through building materials.

A leak from a bathroom upstairs might appear as a damp patch in your living room. A pipe leak in one wall might show up in a completely different room. Painting over the stain or treating the visible area won't solve anything if the source is elsewhere.

How We Find Hidden Leak Sources

When you call us about a damp wall, we don't guess. We use technology to trace the water back to its source:

Thermal imaging—shows temperature differences caused by moisture, revealing the path water has taken through the structure.
Moisture meters—measure the moisture content of walls at different points, helping us map the extent of the damp.
Acoustic detection—if we suspect a pressurised pipe leak, we can listen for the sound of water escaping.
Pressure testing—isolating and testing pipe sections confirms which pipe is leaking.

By combining these methods, we can tell you exactly where the water is coming from—not just where it's showing up.

What Happens If You Ignore It?

Damp patches don't fix themselves. Left untreated:

Structural damage worsens over time
Mould growth spreads (a health hazard)
Decorations are ruined repeatedly
Repair costs increase significantly
Property value decreases

The sooner you find and fix the source, the less damage you'll have to repair.

When to Call a Professional

If you've ruled out condensation (improved ventilation doesn't help) and can't see an obvious external cause, there's a good chance you have a hidden leak. That's when it's time to call for professional leak detection.

We'll find the source quickly, without making exploratory holes in your walls, and give you a clear report so your plumber knows exactly where to repair.

Damp Patches on Walls? Here's What's Causing Them