01What mould actually needs
Three things: moisture content above about 20%, a temperature between roughly 4°C and 38°C, and time. Wood provides the food. Remove any one of the three and nothing grows.
Temperature is not controllable in a yard. Time is not controllable in a supply chain. Moisture is the only variable anyone can actually manage, which is why every practical solution comes back to it.
| Wood condition | Typical moisture | Mould risk |
|---|---|---|
| Freshly sawn green lumber | 40–80% | High |
| Air-dried, outdoor stored, wet climate | 22–30% | High |
| Air-dried, covered storage | 14–19% | Low |
| Heat treated | 15–20% | Low |
| Kiln dried | ≤19%, often 12–15% | Very low |
02Why it matters even though it is harmless
Surface mould on a pallet deck is cosmetic. It does not weaken the wood, it does not migrate into sealed packaging, and in most cases the organism is dead by the time anyone sees the mark. The staining that remains is called mould shadow.
None of that helps at a food plant gate. Visible mould or staining is the single most common reason a load gets rejected in a food and beverage operation, and arguing about whether it is structurally harmless is not a conversation anyone wins at a receiving dock.
“I have never had an auditor accept 'it's only cosmetic.' Not once in eleven years.”
03Where the moisture actually comes from
When a customer reports mould, we investigate the chain rather than assume the pallet arrived that way. In the great majority of cases it did not.
- Outdoor storage at the receiving end. A dry pallet stored uncovered for three wet weeks is no longer a dry pallet. This is the single most common cause.
- Wrapped while wet. Stretch wrap over a damp load traps moisture against the wood at ambient temperature. That is an incubator.
- Condensation cycling. Cold chain product moving in and out of temperature creates surface water repeatedly.
- Wet product. Produce, and anything washed before palletising, brings its own moisture.
- Genuinely damp supply. It happens, particularly with air-dried stock out of a wet region. It is the minority case.
04Specifying against it
If mould matters to your operation, put moisture in the specification. Almost nobody does, and then everybody is surprised.
- Specify heat treated stock. The process drops moisture to 15–20% as a side effect and costs $1.10–$1.90 per pallet.
- Or specify kiln dried with a documented moisture certificate, where a customer or regulator requires evidence.
- Add an appearance clause for mould shadow — historic staining that treatment killed but did not remove.
- Specify covered storage at both ends, in writing, and mean it.
- Set a maximum dwell time for wrapped loads in warm conditions.
The A-clean sort we run screens for mould shadow specifically, alongside stain, paint and raised splinters. It costs about $1.40 a pallet and removes most of this problem at the gate.
05The weight argument nobody makes
There is a second reason to care about moisture that has nothing to do with mould. Water is heavy. A 48x40 pallet that has sat in the rain can carry 6 to 10 lb of water it did not have when it was dry.
On a trailer carrying 26 loaded pallets, that is 156 to 260 lb of payload you are paying to move and cannot sell. For anyone weighing out rather than cubing out, specifying dry stock is a freight decision before it is a quality one.
