Keeping mold off pallets
Mold needs moisture. Wood with a moisture content below 20% will not support mold, mildew, decay or fungus, so the whole job is keeping stacks dry.
Where mold comes from
Mold grows on wood that stays damp. A pallet left on bare ground through a Michigan spring, a stack under a leaking roof, or pallets loaded into a closed van straight out of a kiln all hold moisture long enough to start it. Once it has started, a wet stack keeps it going.
| Situation | Why it molds | What helps |
|---|---|---|
| Outside on the ground | Ground moisture wicks up into the bottom boards | Keep stacks off the ground on a pad or on other pallets |
| Covered tightly with plastic | It traps moisture instead of shedding it | Cover the top and leave the sides open to air |
| Packed tight in an indoor stack | No air moves between the pallets | Even slight air velocity, a few feet per second, can help |
| Loaded hot into a van | Heat-treated pallets loaded into trailer vans while still hot are susceptible to mold | Let them cool and dry first |
Heat treatment does not make wood immune
HT kills pests by heating the core to 56 degrees Celsius for 30 minutes. It does not dry the wood for good and does not leave a protective layer. A heat-treated pallet that gets wet can mold like any other. The stamp on it says it was treated, not that it is clean. Reading the stamp.
A storage routine that works
Raise it
Put the bottom pallet on a pad, a slab or a pair of boards, never straight on dirt.
Cover the top
A roof or a sheet over the top keeps rain off. Leave the sides open.
Let air through
Do not wall a stack in. A gap between stacks and between the stack and the wall helps.
Rotate
Use the older pallets first. A pallet that sits a year has a longer window to get damp.
Check by hand
Damp wood feels cool. A musty smell means it has started.
Food docks and mold
Food wholesalers start with a clean, dry Grade A for a reason: a pallet that went through a damp week is a risk next to produce. If a pallet is moldy, pull it from use. Mold is not a repair problem; it is a reason to take the pallet out of the flow and place it with a recycler. See pallet recycling.
Questions about mold
How do I stop it?
Keep wood below 20% moisture, and keep air moving past it.
Does heat treatment help?
No. It does not make wood immune, and hot pallets loaded into vans can grow mold.
Can I clean it off?
Surface mold can be removed. Deep mold means a core.
A fan is cheap
Even a slight air velocity of a few feet per second helps prevent mold on stored pallets. A box fan at the end of a covered stack is enough.
Reading the signs
Look for gray or green fuzz, a musty smell and dark patches on the underside of boards. Any of them means moisture has been present for days. Remove the pallet from food service immediately.
Fans
Use a fan.