The Problem with Moisture in Timber
Freshly cut timber — sometimes called green timber — contains a significant amount of water. Depending on the species, freshly sawn wood can have a moisture content (MC) of anywhere between 50% and over 100%. This moisture has to go somewhere, and how it leaves the wood matters enormously for the final product.
As timber dries, it shrinks. If it dries unevenly — which is almost inevitable without controlled drying — different parts of the board shrink at different rates, causing warping, cupping, splitting, and checking. Controlling the drying process is what separates quality structural and finished timber from timber that fails in service.
How Air Drying Works
Air drying is the simplest method: sawn timber is stacked in open or covered storage with spacers (stickers) between each layer to allow air circulation. The wood dries naturally as ambient air carries moisture away from the surface. There is no heat source, no humidity control — just time.
The main advantage of air drying is cost: it requires no machinery, no fuel, and minimal labour. The main disadvantage is time: depending on species and thickness, air drying can take months to years to bring timber to usable moisture levels. A 25mm board of rubberwood might take 3–4 months to reach 18–20% MC outdoors in Sri Lanka — and will rarely get below 15% without kiln drying.
- Slow — typically months to years depending on species and thickness
- Cannot achieve consistent low MC (below 12–15%) without kiln finishing
- Subject to seasonal variation and ambient humidity
- Risk of surface mould, staining, and insect attack during drying
- Low capital cost, suitable for rough construction timber
How Kiln Drying Works
Kiln drying uses a controlled environment — elevated temperature, humidity regulation, and airflow — to accelerate and control the drying process. Timber is loaded into a kiln chamber, and a drying schedule is programmed based on the species, thickness, and target moisture content. The schedule typically starts with higher humidity and lower heat to dry the surface slowly, then progressively reduces humidity and increases temperature to draw moisture from the core.
The result is timber that reaches a precise target MC — typically 12–15% for furniture and joinery, or 15–18% for construction — in days rather than months, with far less degradation than uncontrolled drying. Kiln drying also kills insects and their eggs, providing pest protection as a by-product of the process.
- Fast — typically 3 to 12 days depending on species and target MC
- Consistent, precise moisture content across the entire batch
- Reduces shrinkage, warping, and splitting in service
- Kills surface and internal insects at treatment temperatures
- Required for furniture, joinery, flooring, and export applications
Which Method Should You Use?
For rough structural applications — roof purlins on a simple warehouse, scaffold planks, temporary hoarding — air-dried or partially dried timber may be acceptable, provided the structure allows for some movement and the timber grade is appropriate.
For anything that requires dimensional stability — furniture, door and window frames, finished flooring, structural beams in tight-tolerance framing, or export timber — kiln drying is not a recommendation, it is a requirement. Timber that moves after installation costs more to fix than the drying would have cost in the first place.
St. Xavier Timber's industrial kiln brings timber to a target MC of 12–15% with temperature and humidity monitoring throughout each cycle. We work with rubberwood, mahogany, teak, pine, and most domestic and imported hardwood species.
Can Air-Dried Timber Be Kiln Finished?
Yes — and in some cases it makes economic sense. Timber that has been air-dried to 18–20% MC over several months can be loaded into a kiln for a shorter drying cycle to bring it to the final target MC. This reduces kiln time and fuel cost while still achieving a consistent, controlled result.
For manufacturers running large volumes, combining air drying yards with kiln drying capacity is a practical approach to managing stock throughput. Talk to our team about your volume and timeline requirements — we can advise on the most cost-effective approach.