Humidity, Basements And The Mildew Line

Clothes stored in basements, garages and closets on exterior walls develop a characteristic musty smell. The cause is the moisture content of the air, and it has a fairly sharp threshold.

Mold needs moisture in the air, not standing water

Mold spores are present everywhere and germinate when they find enough moisture. That moisture comes from humidity in the surrounding air rather than from anything spilled.

Above a certain relative humidity, sustained over time, growth becomes possible on almost any surface including clean fabric.

Below that level growth stops, which is why the same garments can sit for years in a dry closet and for one summer in a damp one with very different results.

Natural fibers feed the process

Cotton, linen and other cellulose fibers are digestible by mold, so growth on them consumes the fabric and leaves permanent staining and weakened areas.

Synthetics are not a food source, but mold grows readily on the soil, body oils and sizing present on their surface.

Which means washing before storage matters more than fiber choice. A clean synthetic and a clean cotton both resist far better than either does when soiled.

Cold surfaces create local damp

Air holds less moisture as it cools, so warm humid air meeting a cold wall or floor deposits water there.

An exterior closet wall, a concrete basement floor and an uninsulated attic roof all create zones that are damper than the room average.

This is why the affected garments are usually the ones pressed against a wall or sitting directly on the floor, rather than everything in the space.

Sealed containers cut both ways

An airtight bin keeps humid room air out, which is the intended benefit, and it also traps whatever moisture the contents held when they were packed.

Sealing a garment that is even slightly damp creates a small enclosed environment at high humidity, which is close to ideal for growth.

Garments must be fully dry before sealing, and containers are better stored raised off a concrete floor where condensation collects underneath.

The remedies are about air, not scent

Desiccant packs absorb moisture and work within a sealed container, though they saturate and need replacing over a long storage period.

A dehumidifier addresses the room and therefore everything in it, which is the only approach that works for open storage.

Scented products mask the odor without altering the humidity, so the growth continues and the fabric damage accumulates behind the smell.