Damp walls, mould and peeling paint: what causes them and how to fix them

Black spots creeping up the bathroom wall. Paint bubbling just above the skirting. A white powder pushing through fresh paint on a new house. Every one of these is a moisture problem first and a paint problem second.

We get these questions every week, from Kisumu to Mombasa to the cold, wet highlands around Limuru and Nyeri. Here is the honest answer: no paint will permanently fix a wall that keeps getting wet. The right paint will help a sound wall stay dry and clean, and it will resist mould far better than the wrong one. But first you have to find out where the water is coming from.

Step 1: read the wall

Different damp problems leave different clues.

Tide marks and bubbling near the floor, worst after rain. This points to rising damp: ground water moving up through the wall because the damp-proof course is missing, bridged or damaged. Common in older houses, and where outside soil or paving has been built up against the wall.

Damp patches high on the wall or on the ceiling. Usually a leak: a roof sheet, a gutter, a flashing, a valley or a plumbing pipe. Patches often appear some distance from the actual leak, because water runs along the inside before showing.

Mould in corners, behind wardrobes, on bathroom and kitchen ceilings. Condensation. Warm, moist air from showers, cooking and drying clothes hits a cold wall and turns to water. Very common in cooler towns and in rooms with poor airflow.

Damp patches on the outside face of a wall, worst on the side that gets the rain. Rain soaking through cracked or porous plaster.

White, fluffy or powdery salts on new walls. Efflorescence. As fresh plaster and blockwork dry out, water carries natural salts to the surface. It pushes paint off from behind and is most common in the first months of a new build.

Paint peeling in flakes with no damp at all. Usually preparation: paint applied over chalky old paint, dust, or fresh plaster without a suitable undercoat.

Step 2: fix the cause

Do this before you spend anything on paint.

• Leaks: repair the roof, gutters and plumbing first. On mabati roofs, seal leaking nail holes and laps; our bitumen-based Roof Sealer is made for that. Our mabati roof guide covers it in detail.
• Rising damp: lower soil or paving that is above the damp-proof course, clear drainage away from the wall, and get a builder to assess the damp-proof course itself. This is building work, not painting.
• Rain penetration: fill cracks, repair hollow plaster and fix broken sills and copings.
• Condensation: improve ventilation. Open windows after showering and cooking, fit extractor fans or vents, and leave space between furniture and outside walls.
• Efflorescence: let new walls dry out. Brush the salts off dry with a stiff brush (do not wash them back into the wall), wait, and repeat until they stop coming. Only then paint.

Once the cause is fixed, give the wall time to dry out properly. A wall that has been soaked for months can take weeks to dry.

Step 3: clean off mould properly

Painting over mould just hides it for a while. The spores grow back through the new paint.

1. Wear gloves and eye protection, and open the windows.
2. Treat the affected area and a margin around it with Maroo Fungal Wash. It is formulated to neutralise active fungal growth on masonry, plaster and wood and leaves a clean surface for the new coating. Follow the dilution and contact time on the label. [Placeholder to confirm: dilution and contact time, and whether to rinse.]
3. Scrub off the dead growth and let the wall dry completely.

Step 4: repair the surface

• Scrape off all loose, bubbling and flaking paint back to a firm edge.
• Fill cracks with Maroo Crack Filler, an elastomeric filler that stays flexible, for concrete, plaster and masonry.
• For walls that need skimming, Wall Matt Filler is a wall putty made to protect against flaking, with water resistance and strong binding to the base plaster. It comes in 25 kg bags.
• Sand smooth and dust off.

Step 5: choose the right paint

Exterior walls

On outside walls you want a coating that keeps rain out but lets moisture already in the wall escape. If a wall cannot breathe, trapped water pushes the paint off.

Weather Guard Silicone Exterior is our premium masonry coating for this job. It uses silicone technology to give strong water-repellent performance with high vapour permeability: rain beads off, while the wall can still dry out. Packs: 20, 4 and 1 litres.

For standard exterior work, Weather Guard Exterior is a water-based matt finish for masonry that covers approximately 12 to 14 m² per litre per coat, depending on the porosity of the surface.

Interior walls and ceilings prone to mould

Master Guard Emulsion (Anti Fungal) is our anti-fungal emulsion for walls and ceilings in rooms where mould is a risk. [Placeholder to confirm: verified specifications for Master Guard from its data sheet before quoting coverage or drying time.]

Kitchens and bathrooms

Here you need a finish you can wipe down. Vinyl Silk Emulsion has a soft sheen and, according to its data sheet, resists grease, oil and stains, so splashes and steam marks clean off without scrubbing the paint away. It covers approximately 11 to 15 m² per litre per coat and can be recoated after 1 to 2 hours.

Wet areas and below-ground walls

Paint alone is not enough where walls are wet much of the time, such as in tanks, basements or shower areas under tiles. Fixosil is a specialist polymer for waterproof cement-based coatings, mixed into a slurry or into cement and sand mortar. Treat this as part of the building work, ideally specified by your builder or a waterproofing contractor.

Step 6: paint it right

• Make sure the wall is dry. If in doubt, wait longer.
• Apply two even coats, letting each dry as the data sheet says.
• Keep the room ventilated while it dries.
• Do not paint outside walls in rain, or when rain is expected before the coat has dried.

When to call in help

If patches return after a proper repaint, the moisture source has not been fixed. That needs a builder or plumber, not more paint. For advice on the paint system for a difficult wall, book a consultation with our team.

Frequently asked questions

What is the best paint for damp walls in Kenya? There is no paint that cures damp. Fix the cause first. Then use a breathable, water-repellent exterior coating such as Weather Guard Silicone outside, and an anti-fungal emulsion such as Master Guard inside where mould is a risk.

Why is my new paint peeling? The most common reasons are moisture in the wall, efflorescence salts on new plaster, and painting over dust or chalky old paint without proper preparation.

Can I paint over mould? No. Kill and remove it first with a fungal wash, let the wall dry, then repaint. Otherwise it grows back through the new paint.

What is the white powder on my new walls? Efflorescence: natural salts carried out of fresh plaster and blockwork as they dry. Brush it off dry and let the wall finish drying before painting.

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