Identify the surface and follow the current instructions for your exact products. Do not sand or strip uncertain old coatings. Read the safety guide before disturbing materials.
A stain is a clue, not a diagnosis
A mark after rain, mould at a cold corner and a stain below a bathroom may have different causes. More than one cause can be present. The pattern, timing and building details matter, and a handheld moisture reading alone does not identify the source.
Record when the problem appears, whether it follows rain or room use and whether it changes with the season. Check obvious accessible issues such as overflowing gutters or a leaking fitting without disturbing unsafe materials.
Resolve moisture before choosing paint
Leaks need repair. Condensation often involves a combination of moisture production, ventilation, heating and cold surfaces. Maintain working extraction and do not block intended ventilation. Building defects or persistent problems deserve a proper assessment.
Anti mould paint is not a cure for a damp building. Painting over visible growth does not remove the source or make the substrate ready. Follow suitable current health guidance and product safety instructions for any cleaning. Never mix cleaning chemicals.
Only then return to decoration
After the cause is resolved, allow the substrate to reach the conditions required by the coating system. Damaged plaster or decayed timber may need repair or replacement. A compatible stain block can address certain remaining marks, but cannot stop new water arriving.
Keep a record of repairs and watch the area through the conditions that previously caused the issue. If the mark returns, investigate again rather than adding another coat.
Common mistakes
- Treating stain block as waterproofing.
- Dry brushing mould into the air.
- Assuming every low wall stain is rising damp.
Extensive or recurring mould, vulnerable occupants, water near electrics, sagging ceilings or an active leak warrant prompt appropriate professional help. Avoid disturbing contaminated material.
Sources & further reading
Original general guidance from Aethos, informed by the resources below. These references cover relevant safety, materials or techniques, not a specification for your property. Product examples are not paid recommendations.
- Zinsser: Bulls Eye 1 2 3 technical information (opens in a new tab)
An example of why preparation, substrate suitability and recoat instructions are product specific.
- SPAB: limewash (opens in a new tab)
Traditional finishes, suitable substrates and caring for older buildings.
- HSE: asbestos guidance (opens in a new tab)
Identifying potential asbestos risks before disturbing building materials.