Mould on pallets: moisture, storage and food loads
Wood with a moisture content below 20 percent will not support mould, mildew, decay or fungus. Above it, a pallet stored damp can grow mould within days.
Moisture content, in plain words
Moisture content, written MC, is the share of a board's weight that is water. A pallet sitting in a West Michigan yard through a wet week can climb well above 20 percent. A dry warehouse floor brings it back down slowly.
Three ways pallets get damp
- Rain and ground contact in an uncovered yard
- Stacking on wet pallets or damp concrete
- Heat-treated pallets loaded into a trailer van while still hot, which trap moisture as they cool
Heat treatment does not make wood immune to mould. A freshly treated pallet is dry, but once it is wrapped in a van it can sweat.
What helps
Even a slight air velocity, a few feet per second, can keep stored pallets from moulding. Airflow beats a tarp in a sealed stack. Stack off the ground and leave gaps.
For a food dock
A food load wants dry wood, no visible growth and no musty smell. If a stack has a green or black stain in the grain, do not send it to a food room. See clean, dry pallets.
| Question | A good answer |
|---|---|
| Where were they stored? | Indoors or under cover |
| When were they last wet? | Not in recent weeks |
| Were they treated and loaded hot? | No, or they cooled first |
What mould looks like on wood
Early mould shows as grey or green fuzz, or black speckling that follows the grain. It can look like dirt, but it comes off as a smear rather than a flake. Sour or musty smell is often the first sign, and a nose is a quicker test than a moisture meter.
Moisture meters
A pin-type meter pushed into a board reads moisture content directly. A reading under 20 percent is the line to stay below. Take readings at several boards, including the bottom ones, which stay wet longest. A buyer who wants numbers can ask a seller for them.
Then see the clean-food pallets page for the buying side.
Ventilation in a yard
Stack pallets in rows with gaps between them so air can flow. Keep them off bare ground with timbers beneath. A tarp that touches the stack holds moisture in; a roof with open sides does not.
A seasonal pattern
In West Michigan, spring is a dangerous season. Snow melt and cold nights leave pallets damp, then warm days encourage growth. Check outdoor stacks in April and May.
What to do about a damp pile
If a stack looks damp or smells musty, move it under cover and let air reach every layer. Wood that dries below about 20 percent moisture stops supporting mould.
Do not ship mouldy pallets to food, medical or paper customers. A pallet that has visible growth should go for recycling, not for resale.
Source: Pallet Enterprise, "Keys to controlling mold on lumber pallets" (read 10 November 2026). Last reviewed 12 November 2026.
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Last reviewed 12 November 2026.