All our timber is air-dried. The timber is milled into planks, stacked on a flat base between stick battens and the top of the stack then covered from the sun and rain. Aside from being lower in cost to produce in terms of not having to pay extra for kiln drying, it also means we are not creating a carbon footprint. The science in air-drying is an interesting process and it’s very rewarding to find that the more attention to detail paid at the beginning, the better the quality of timber at the end.
Below are extracts from an excellent guide to timber drying – this provided me with essential information when starting up:
This is a method of drying timber by exposing it to natural atmospheric conditions. As such there is no control over drying rate as this will be determined by the prevailing weather (temperature, relative humidity, rainfall and wind speed), which will vary considerably between winter and summer. Some control over drying times and degrade can be achieved by correct stacking procedures of freshly sawn timber.
Air drying does not involve the need to burn fuels to dry wood thus conserving energy and reducing harmful atmospheric emmissions
The obvious advantage of air drying is its low capital cost in comparison to kiln drying procedures. Kiln operators often find that it is more economical to air dry timber to 25% to 30% moisture content if the material is likely to take more than 5 weeks to kiln from green due to its size or the drying characteristics of the timber. However, it is important to remember that air drying can only be used to reduce the moisture
content of timber to around 14 to 20 %. Therefore, for many applications kiln drying or storage in a controlled environment is a necessary final step in the drying process.
Kilns are closed chambers in which air temperature, relative humidity and airflow can be controlled to dry timber to specified moisture content. There are many different types of kilns such as vacuum systems, traditional heat and vent type kilns and radio frequency dryers. The
cost of installing and maintaining kilns may often be prohibitive unless throughput of timber is high. However, if the value of specific species is high enough, it becomes more feasible to kiln dry green timber.
A rule of thumb for the UK is that 25mm (1″) thick material will take one year to dry, 50mm (2″) thick material will take two years to dry and 75mm (3″) thick material will take 3 years to reach equilibrium moisture content by air drying. In addition to thickness, drying times depend on the characteristics of the timber being dried, climatic conditions (temperature and relative humidity) and airflow through the stack. Some timbers will have higher green moisture content than others. Furthermore, heartwood and sapwood from the same tree may have very different drying characteristics.