What Is Moisture Content?
Moisture content (MC) is the weight of water in wood expressed as a percentage of the wood's oven-dry weight. A board with 12% MC contains water equal to 12% of its dry weight. This number is critically important because wood expands and contracts as its moisture content changes — a phenomenon called wood movement.
New kiln-dried lumber is typically sold at 15-19% MC for framing and 6-8% MC for interior finish applications. Reclaimed lumber that has been air-drying in a structure for decades often stabilizes at 8-14% MC depending on the climate it was in.
Measuring MC in Reclaimed Wood
Pin-type moisture meters are the most practical tool for checking reclaimed lumber. Insert the pins into the wood (avoiding knots and end grain) and read the display. Take readings at several points along the board — reclaimed wood may have variable MC if different parts of the board were exposed to different conditions.
For critical applications like flooring and cabinetry, we recommend keeping MC below 8%. For general interior use, below 12% is acceptable. For exterior applications, 12-15% is fine since the wood will equilibrate with outdoor humidity anyway.
Kiln Drying Reclaimed Lumber
If reclaimed lumber tests above your target MC, kiln drying is the solution. Our solar-assisted kiln brings lumber to 6-8% MC in 2-4 weeks depending on species, thickness, and starting MC. Kiln drying also kills any insects or larvae that may be present in the wood — an important consideration for reclaimed material.
Air drying is an alternative but takes much longer (roughly one year per inch of thickness) and does not achieve MC levels below about 12% in most climates. For any interior finish application, kiln drying is strongly recommended.