Mould control

Mould spores are present in essentially all indoor air all of the time. They are harmless until they find a surface with enough moisture to germinate on. So mould growth is not really a contamination event, it is a moisture indicator — it grows precisely where a surface is staying wet enough for long enough.

That is why cleaning alone reliably fails. Wiping it off with bleach removes the visible growth and changes nothing about the conditions, so it returns on the same wall, in the same corner, usually within a season.

In the great majority of homes the underlying condition is condensation. Sometimes it is a leak, penetrating damp, or a cold bridge at a specific junction. Establishing which one is the difference between a fix and an annual ritual.

Damp and mouldy homes are associated with respiratory problems, and the risk is meaningfully higher for people with asthma or allergies, for those who are immunocompromised, and for infants and the elderly. That is well established and worth taking seriously.

It is also worth not overstating. The commonly encountered household moulds are a genuine irritant and aggravator rather than an acute poisoning risk to a healthy adult, and the alarming end of what is sold online trades on fear. The sensible position is that mould in a home is a problem that should be fixed rather than lived with, and that it should be fixed by removing the moisture rather than by repeated chemical warfare on the surface.

Treatment and safe removal of the existing growth, using fungicidal products appropriate to the surface rather than bleach, which discolours the growth without reliably killing what has penetrated a porous substrate. Where growth has taken hold in absorbent material — plasterboard, insulation, badly affected sealant — cleaning is not sufficient and the material comes out.

Then the actual work: identifying and correcting the moisture source. In practice that usually means the ventilation and thermal measures set out under condensation control, or tracing and stopping an ingress. Without that step, the treatment is cosmetic and temporary, and I will say so rather than take the money for it.