Why Does Mould Keep Coming Back?

It is one of the most frustrating problems for homeowners, landlords and tenants alike: you clean the mould, repaint, and within weeks the black spots are back. If that sounds familiar, the issue is almost never the cleaning product. It is that the conditions which let mould grow have not changed.

Reason 1: the moisture source is still there

Mould spores are everywhere in the air. They only take hold where a surface stays damp for long enough. Whether that moisture comes from condensation, a leak or water penetrating the wall, if it continues, mould will regrow however thoroughly the surface is cleaned.

Reason 2: cold spots on walls and ceilings

Corners, window reveals, the area behind wardrobes and ceilings below unheated lofts are often colder than the rest of the room. Warm, moist air condenses on these surfaces first. This is why mould so often returns to exactly the same place. Improving insulation in those spots, or fitting an anti-condensation or graphite thermal liner, raises the surface temperature so condensation no longer forms.

Reason 3: not enough ventilation

Modern double glazing and draught-proofing keep heat in, but they also keep moisture in. Without working extractor fans, open trickle vents or another form of controlled ventilation, humidity builds up. Extractor fans in kitchens and bathrooms, and Positive Input Ventilation for the whole house, are often the long-term answer.

Reason 4: the mould was only bleached

Bleach removes the colour but may not kill spores that have rooted into porous surfaces. Using a proper fungicidal treatment and a mould-resistant finish gives a much cleaner start.

Reason 5: the wrong diagnosis

Sometimes what looks like condensation mould is actually being fed by penetrating damp from a defect outside – a blocked gutter, cracked render or failed pointing. Treating the inside alone will never fix it.

The root-cause approach

Our 3-step mould eradication process starts with a structural survey and detailed report, including external checks of pointing, ventilation, radiator placement and property orientation, plus temperature, humidity and dew-point readings. We then remove the mould and put the right prevention measures in place. Because the cause is dealt with, mould eradication comes with a 12-month guarantee against it returning.

Related help

If this sounds like your home, our mould removal and remediation service explains how we diagnose and treat it in practice. You may also find How to Get Rid of Mould Permanently and Mould Near a Bedroom Window useful.