If you live in a property with lime or clay plaster, you have a massive advantage in the fight against moisture. Unlike modern drywall or “plastic” paints that trap humidity, lime and clay are breathable. They act like a lung for your house, absorbing excess moisture when it is humid and releasing it when it is dry.
However, the winter of 2026 has pushed even these resilient materials to their breaking point. Here is why this year is different, and how to manage it.
1. The “Wake-Up Call” of Winter 2026
The start of 2026 will be remembered in Southern Spain for the relentless “train of storms” and the atmospheric rivers that drenched Andalusia. This wasn’t just rain; it was saturation.
For traditional Spanish homes, this created a perfect storm of problems:
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Clay Soil Saturation: The ground in Southern Spain is often clay-heavy. After months of heavy rain, the soil swelled and became fully saturated, pressing wet dirt directly against building foundations.
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The “Wick” Effect: Most older Spanish properties were built without a Damp Proof Course (DPC). Without this plastic barrier, the masonry acts like a wick. Because the clay soil outside is waterlogged, the walls are drawing gallons of water up from the ground (capillary action) faster than they can evaporate it.
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The Consequence: Your walls are currently fighting water from two directions: the humid air inside and the rising damp from the ground. This makes the strategies below not just helpful, but essential for saving the building fabric.
2. Can Mould Still Grow on Lime and Clay?
Yes. While lime is naturally alkaline (which burns mould spores) and clay regulates humidity, they can be overwhelmed.
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The 2026 Problem: Because the walls are so saturated from the ground up, the lime is effectively “diluted,” and its ability to fight mould weakens.
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Surface Food: Mould is likely eating the dust, cooking oils, or organic debris sitting on top of the wet plaster.
3. The Golden Rule: The 55/15 Balance
To stop condensation—the water that allows mould to thrive—you need to manage both heat and humidity. The most effective strategy is the 55/15 Rule:
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Humidity: Keep your relative humidity around 55%.
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Heat: Never let the house drop below 15°C (59°F), even at night.
Why is this critical now? If you turn off the heating at night, your damp walls will get very cold. When the heating comes on in the morning, warm air hits the cold, wet masonry, causing massive condensation. Maintaining a steady background temperature of 15°C helps the walls “sweat out” the moisture they draw up from the clay soil.
Tip for Unheated Rooms: If you use a dehumidifier in a cold room (under 15°C / 59°F), choose a Desiccant model, not a Compressor Model. Standard compressor units will freeze up in cold houses; Desiccant units keep working and even blow out warm air, which helps dry the damp masonry.
4. Daily Habits to Stop Moisture
You produce litres of water a day just by living. Don’t add this to the burden your walls are already carrying.
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The “Shock” Method: Don’t leave a window cracked all day. Instead, open windows wide for 10 minutes twice a day. This replaces wet air with dry air without cooling the stone walls.
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Furniture Gap: Pull wardrobes and sofas 10cm (4 inches) away from external walls. The walls need to breathe now more than ever; pushing furniture against them will trap the rising damp and cause rot.
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Drying Clothes: Do not dry wet clothes on radiators.
5. How to Clean Mould Safely
If you find a patch of mould, be extremely careful. The wrong cleaner can damage your wall.
If your wall is LIME:
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NEVER use Vinegar. Vinegar is an acid; Lime is an alkaline base. Vinegar will eat into the plaster.
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Use: 70% Isopropyl Alcohol (Rubbing Alcohol) or clear Ethanol.
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Method: Lightly mist the area, wait 10 minutes, and effectively blot it with a clean cloth. Do not scrub hard.
If your wall is PURE CLAY:
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You can use Vinegar. A 50/50 mix of white vinegar and water works well.
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Method: Dampen a cloth and gently dab the mould away.
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Warning: Clay softens when wet. Do not soak the wall; it will turn back into mud. Dry the area immediately with a fan.
Summary
The winter of 2026 has been historic, and your walls are soaking wet from the ground up. You cannot stop the rain, but by keeping the house at a steady 15°C and using desiccant dehumidifiers, you can help your lime and clay walls “exhale” that ground water before it turns into mould.