The weight of water in pallet lumber expressed as a percentage of the wood's oven-dry weight, affecting durability, weight, mold risk and performance in cold-chain or food applications.
Detailed Definition
Moisture content (MC) is the weight of water in wood divided by the weight of the same wood when oven dry, expressed as a percentage. Because the base is the dry wood, freshly sawn green lumber can have MC above 100 percent in some species. As wood dries below its fiber saturation point, it starts to shrink and gain stiffness. Softwood lumber sold as KD19 has been kiln dried to 19 percent MC or less. For pallets, MC affects weight, shrinkage, nail holding, mold risk and suitability for food or export shipments.
How moisture content is measured
The reference method is oven drying: weigh a sample, dry it in an oven until its weight stops changing, and calculate the water lost as a share of the dry weight. ASTM D4442 covers direct moisture measurement methods for wood. In the field, people use handheld meters. Pin meters measure electrical resistance between two pins, and pinless meters measure a field in the surface layer. Meters must be set for species and temperature, and they read the outer part of thick pieces most strongly, so take several readings away from board ends.
Why pallet buyers care
- Mold: wood kept wet in warm, closed spaces is prone to mold, so dry wood is safer for food, pharmaceutical and export loads.
- Shrinkage: green pallets shrink as they dry, which can loosen nails and change dimensions.
- Weight: water adds weight, increasing freight and handling effort.
- Cold chain: wet pallets moved into freezers can ice up and damage packaging.
Heat treatment for ISPM 15 is about pest control and does not set a final MC. If you need dry pallets, specify a maximum MC, the measurement method and where on the pallet it is checked.
Related Glossary Terms
Frequently Asked Questions
What moisture content should pallet lumber be?
There is no single required value for general pallets, and many are built from green lumber. Where mold, weight or dimensional stability matter, buyers often ask for dried lumber, and KD19, meaning 19 percent or less, is a common reference point from softwood lumber grading. Set a maximum value that fits your application, say how it will be measured, and agree on what happens if a delivery tests above it.
Does heat treating a pallet dry it out?
Heat treatment for ISPM 15 only requires the wood core to reach 56 C for at least 30 continuous minutes, which is enough to kill pests but often not long enough to dry the wood much. Some moisture is lost, but a green pallet can still be wet after treatment. Kiln drying is a longer process designed to bring wood to a target moisture content. If you need both, specify both.