Why pallets go mouldy, and how to stop it

01 What causes it

• Storage outdoors on bare ground, where water wicks up.
• Stacking before wood has dried.
• Loading a heat-treated pallet into a trailer while still hot.
• Packing tight so air cannot move.

02 Heat treatment is not a cure

Heat treatment is a pest-control step. It does not make wood immune to mould, and a pallet that leaves the kiln warm and is shut in a van can sweat. If your load is going to sit in a container for weeks, ask for dry stock and for time to cool.

03 Storing pallets

1. Keep them off the ground.
2. Cover the top, not the sides.
3. Leave air gaps between stacks.
4. Check a sample with a moisture meter if the load matters.

04 Pittsburgh's climate in one line

River valleys hold damp air, and a back lot near the Allegheny, the Monongahela or the Ohio will see more of it than a hilltop dock. That is a reason to store indoors or under a roof, not a measurement.

05 Spotting mould

• Grey or green patches on the deck.
• A musty smell on opening a trailer.
• Dark staining at the board ends.
• Softness when pressed with a thumbnail.

06 How fast mould starts

Mould spores are everywhere. With oxygen, moisture, a suitable temperature and a food source, they can germinate in 24 to 48 hours, and wood is a food source. Growth is possible as low as 32 degrees Fahrenheit and speeds up between 66 and 90 degrees. Kiln-dried lumber is below 20% moisture but can mould quickly once it gets wet, and a closed trailer left at a customer site acts as an incubator.

07 Cleaning and treatment

Pallet Enterprise reports that a solution of two parts water to one part household detergent kills or removes mould and stays effective for three to five days, and that Virginia Tech suggests bleach solutions where chemical exposure is not a concern. Fungicide dips applied to lumber work better than sprays on finished pallets and buy time until wood dries.