Damp walls: find the cause first

What the damp is telling you

The height, place and season of a damp patch usually point to its cause, so look carefully before you scrape anything.

Condensation: water from the air inside

Condensation happens when warm, moist indoor air meets a cold wall and leaves water on it. It is the usual cause of black mould in closed rooms.

• Cooking, showers and drying clothes indoors put a lot of water into the air, and Alexandria's air is humid already.
• Extractor fans in the kitchen and bathroom that vent outside, and opening the windows daily, do more than any paint.
• Keep wardrobes and sofas a little away from cold outer walls so that air can move behind them.
• Clean mould with a suitable anti-mould wash, let the wall dry, then repaint with a breathable paint. An anti-mould additive helps, but it does not replace ventilation.
• A dehumidifier helps in flats that stay closed for long periods.

Leaks: from your pipes or the neighbours'

A leak gives a patch that keeps growing or comes back in the same place, and it must be found and repaired before any work on the wall.

• Close every tap and watch the water meter. If it still moves, there is a leak on the supply side.
• Damp that grows when a bathroom is used points to a drain, a shower tray or failed floor waterproofing.
• A plumber can pressure-test the pipes and use a moisture meter to trace the wet area without breaking open every wall.
• If the water comes from the flat above, take dated photos, speak to the neighbour and the building's occupants' union, and agree the repair in writing. If that fails, take legal advice.
• After the repair, let the wall dry fully before re-plastering or painting.

Waterproofing for bathrooms and roofs is covered on our waterproofing page.

Rising damp on ground floors

Rising damp is moisture from the ground drawn up into the base of the walls. It mainly affects ground floors and basements without a working damp-proof layer.

• First make sure it really is rising damp: many cases that look like it are leaks, condensation, or outside ground that sits higher than the floor inside.
• Lower the ground outside, or slope it away from the wall, and make sure rainwater and garden irrigation drain away from it.
• Dense cement render and gloss paint at the base of a wall can trap moisture and push it higher, so they may need to come off.
• A new damp-proof barrier, such as a chemical injection, is specialist work. Have a specialist assess the wall and explain the method before you agree to it.
• Then re-plaster with a render suited to damp, salty walls, and finish with a breathable paint.

The white salt on the wall

The white powder or crystals on a damp wall are salts left behind as the water evaporates. They are a symptom of moisture, not a separate problem.

• The salts can come from the bricks, the mortar, sand that was not washed, the ground, or sea air that settles on façades near the shore.
• Brush them off dry. Washing them puts water back into the wall.
• They return as long as water keeps moving through the wall, so stop the source first.
• Old plaster that is full of salt usually has to come off and be replaced, or the new paint will blister again.

Before you paint: the right order

Repairing a damp wall is a sequence, and skipping a step is why damp comes back.

1. Find the cause

   Use the signs above, with a plumber or a specialist where needed.

2. Fix the source

   Repair the leak, improve the ventilation, correct the outside levels or treat the rising damp.

3. Let the wall dry

   Drying takes time, longer for thick walls and in winter. Painting a wet wall traps the water.

4. Remove what is damaged

   Scrape loose paint, brush off salts, and take off plaster that is soft, hollow or salty.

5. Re-plaster

   Use a mortar suited to the wall and its exposure, made with clean, washed sand.

6. Paint with a breathable system

   Use paint that lets the wall breathe. A sealing paint over a wall that is still wet only moves the damp somewhere else.

When to call a specialist

Call a specialist when the damp is structural, near the electrics or keeps coming back, because those cases need more than a painter.

• Cracks that widen, or concrete that is flaking and showing rusty steel: have a structural engineer inspect it.
• Damp near sockets, switches or the distribution board: switch off that circuit and call an electrician.
• Mould spread over large areas, or anyone at home with breathing problems.
• Damp that returns after a repair, or whose source is in another flat or a shared pipe.
• Any plan to inject, tank or seal a wall: ask how the method works, and what happens if the damp comes back.

How Itmam handles damp in a renovation

We visit, measure and give you a written, itemised quotation before work starts. When a wall is damp, treating the cause and redoing the finish should be separate items, so you can see what fixes the problem and what only makes it look good.

Plaster, waterproofing, plumbing and painting are part of our finishing and renovation work, from a single bathroom to a whole old apartment. We work in Alexandria, on the North Coast and in New Cairo.

On a finishing contract you pay each supplier directly, the tax invoice is in your name, and our fee for supervision and execution is agreed in writing.