Painting a wall with mould or moisture is like throwing money away. The paint will hide the problem for weeks, perhaps months, but it will eventually peel, stain or lose its finish. This happens everywhere, from humid coastal regions to apartments with poor ventilation, and the solution is not in the paint itself, but in what you do before the paint reaches the wall.
The most common mistake is applying paint over a surface that is still damaged. Two walls with the same area can be in completely different states. One may be dry, clean and ready for finishing. The other may have rising damp, cracks, active mould or old paint peeling off. That's why before any fixed quote, you need to understand what lies beneath.
The three types of moisture that affect painting
Not all moisture is the same, and each type requires different treatment. Confusing the source of the problem leads to wrong solutions and wasted time and money.
Rising damp climbs from the ground through walls via capillary action. It's common in older properties, especially on ground floors, and appears near skirting boards, forming stains, bubbles in the paint and white powder on the surface (salt efflorescence). If this type of moisture is not stopped at the base, all the paint applied on top will eventually peel off.
Infiltration moisture comes from outside: roofs, facades, poorly sealed windows or leaking pipes. It appears in localised areas, often after days of rain, and leaves yellowish or brownish stains. Painting a wall with active infiltration only works if the source of water entry is first eliminated.
Condensation moisture occurs in poorly ventilated spaces, such as kitchens, bathrooms or bedrooms where clothes are dried. Warm air laden with vapour condenses on cold surfaces, creating an ideal environment for mould. In this case, the solution involves improving ventilation, reducing vapour production and applying suitable paint, but never painting directly over mould without removing it first.
What to do before applying the first coat
Good painting starts long before the brush touches the wall. Surface preparation determines how long the finish will last.
If there is visible mould, it must be removed with specific antifungal product, never just with a damp cloth. Scrubbing hard spreads the spores. After applying the product, let it work, clean with gentle movements and let it dry completely. Only then do you assess whether a second application is necessary.
Cracks and fissures should be opened with a grinder, cleaned and filled with non-shrink filler or mortar. If they are superficial, finishing filler is enough. If they are structural or result from wall movement, the intervention may be more extensive. Ignoring active cracks guarantees they will reappear weeks after painting.
Walls with old paint peeling off need scraping. There's no point applying new paint over a loose base. Preparation may include sanding, application of primer fixative or, in more serious cases, complete removal of the old coating down to the render. The better the base, the longer the finish lasts.
After treating moisture, mould or cracks, the wall needs to be completely dry before receiving paint. Depending on the situation, this period can range from a few days to several weeks. Rushing this phase compromises all the work.
Materials and products that help (or hide the problem)
There are moisture-resistant paints, waterproofing primers and anti-mould products. But none of them solves the root cause. They are supporting tools, not standalone solutions.
If the moisture has been resolved at source, paint with anti-mould additive helps prevent stains from reappearing in at-risk areas, such as bathrooms. But if moisture continues to be active, the paint will peel anyway.
Specific primers, such as base fixative or anti-salt efflorescence, prepare the surface to receive the final paint and improve adhesion. They are especially useful on porous walls, with powder on the surface or that have already been treated for rising damp. But again, they only work if the cause has been eliminated.
Waterproofing paints or those with polysiloxane can be useful in humid environments, but should never be seen as a magic solution. Applying expensive paint to a damaged wall results in exactly the same thing: waste.
Quotes per square metre: why two m² are never the same
When someone asks for a quote per square metre, it's normal to expect a quick and definitive answer. But in practice, that figure is always indicative, never final.
Two surfaces with 20 m² can have completely different quotes. One may be in good condition, ready to paint. The other may have mould, cracks, active moisture and peeling paint. The final price depends on the actual state of the wall, not just the area.
That's why our platform always asks for photos and videos of surfaces before finalising any quote. This practice allows the professional to assess the condition of the wall from a distance, anticipate the type of preparation required and avoid surprises during the work. It doesn't replace an on-site visit, but drastically reduces the risk of unrealistic quotes.
Also, the platform always confirms that the professional is properly registered as self-employed or has a registered company before presenting them as an option. This way, the user doesn't need to chase up paperwork or verify records themselves.
When painting can (and should) proceed
There is no right time to paint while the wall is not ready. Rushing only produces rework.
After eliminating the source of moisture, removing the mould, repairing cracks and ensuring the surface is dry, only then does it make sense to proceed. The appropriate primer for the type of wall should be applied respecting drying time. Only then comes the first coat of paint, followed by the second (or third, if necessary) with sufficient interval between each.
Drying times are not suggestions. They are technical requirements. Applying the second coat before the first is dry results in uneven texture, stains or lumps. And if there's pressure to complete the work quickly, the final result will show it.
When everything is done in the right order, painting lasts for years. When you skip steps, it lasts months. The difference is not in the quality of the paint. It's in the state of the wall when the paint was applied.
