Mold and wooden pallets: a customer education guide.

Mold is a naturally occurring fungus that grows on organic surfaces — wood included — when the right combination of moisture, temperature, and food source is present. On wooden pallets, mold can show up as surface discoloration ranging from grey-green to black and is most commonly seen during shipping or storage in humid conditions.

Mold is not the same as wood decay. Decay structurally weakens the pallet over time. Surface mold does not — it is a cosmetic concern, a humidity indicator, and in some end uses a contamination concern, but it does not compromise the pallet’s load-bearing performance.

Mold requires three conditions simultaneously: moisture above ~20% wood-moisture content, temperatures above roughly 40°F, and any organic surface as a food source. Wooden pallets meet the third condition by definition — so mold growth is entirely a function of moisture and temperature control.

The most common real-world cause is moisture trapped during transit or storage. Pallets shrink-wrapped while still humid, drop trailers parked closed for days in summer, and warehouses with poor airflow are the typical patterns. Less commonly, pallets that were not kiln-dried to the proper moisture content before shipping arrive already prone to mold growth.

Mold typically presents as a surface bloom — patches of grey, green, or black discoloration that wipe partially off, sometimes with a slight fuzzy texture. It often appears on the broad faces of deck boards rather than the cut ends, and is most visible on hardwood pallets where the grain provides contrast.

Not all discoloration is mold. The next two sections cover the two most-common things that are mistaken for mold: dark blue-grey wood staining, and tree-sap surface marks.

Blue-grey wood staining (often called “blue stain” or “sap stain”) is caused by a separate group of fungi that penetrate the wood and color the cells from inside. Unlike mold, staining will not wipe off — it’s inside the wood. Staining is cosmetic, does not affect structural performance, and does not transfer to product.

The quick test: try to wipe the discoloration off with a damp cloth. Surface mold partially wipes off; staining does not. If it’s deep blue-grey and uniform, it’s almost certainly staining, not mold.

Softwood pallets — particularly southern yellow pine and other resinous species — can carry natural tree-sap streaks and resin marks. These present as dark amber or brownish surface stains, sometimes glossy or slightly tacky to the touch. They are entirely natural and entirely structural — sap is part of how the tree grew.

Tree sap usually has a faint pine-resin smell and feels slightly sticky. Mold does neither — mold smells musty and feels powdery or fuzzy, not sticky.

Mold prevention starts with proper kiln-drying — every ePallet new build is dried to 19% moisture content or below before it leaves the cut shop. For operations where mold has been a recurring issue, ePallet offers PQ-80 fungicide treatment as a documented add-on at point of build.

On the operations side: ventilate stored pallets, avoid shrink-wrapping warm-and-humid pallets without airflow, do not store pallets directly on damp concrete, and avoid leaving loaded drop trailers sealed in hot humid weather for more than 48 hours.

The shortlist that prevents most real-world mold issues, drawn from 30+ years of ePallet customer service records:

• Store pallets under cover and with airflow. Outdoor storage is the single largest mold-incidence driver in our service data.
• Specify kiln-dried (KD) pallets to 19% MC or below — and ask your supplier for moisture documentation on every shipment.
• If mold has been an issue, add PQ-80 fungicide treatment to your spec — it’s a documented per-build add-on, not a generic claim.
• Ventilate drop trailers parked over weekends in warm-and-humid seasons. Closed trailers in 90°F humidity create perfect mold conditions.
• Train your receiving team to distinguish mold, staining, and sap before rejecting loads — wood staining is not mold, and rejecting it costs both sides.
• Photograph and document any suspected mold incident and report it to ePallet immediately. We respond per our published Mold Policy.

ePallet’s formal Mold Policy is published as customer-service contractual language. The short version: report suspected mold within 48 hours of receipt, send photos, and we will dispatch a service response. Drop-trailer airflow issues are documented separately as a customer-side responsibility.

The full policy text is in our customer-services package — your ePallet account manager can send it on request, or contact us directly through the form below.