How to Dry Wood to Produce Good Quality Timber
This site provides notes explaining how to dry wood to produce good quality dried timber.
Note that these notes do not address the production of dry wood for the purpose of burning but relate to the drying of (mainly) sawn wood intended for use in construction and the fabrication of furniture and similar wooden products.
Introduction to How to Dry Wood
The notes begin by addressing the reasons for producing dry wood: one very important reason for reducing the moisture content in wood is to ensure that when the wood is put into service a change in the moisture content brought about by environment a product is installed in does not cause the wooden product to shrink or swell. Another good reason to dry wood is to avoid fungal degradation of the wood. A number of other reasons to dry wood are explained.
After giving some important definitions and concepts which need to be understood if dry wood is to be produced efficiently (for example the concepts of “Fibre Saturation Point” and “Equilibrium Moisture Content”) the notes then describe the factors which control the drying of wood. Some of the controllable factors relate to the environment where the wood is dried (such as the temperature and humidity of the air) but to dry wood efficiently and so produce timber of optimum quality the internal structure of the wood must be appreciated. Consequently the notes also include an introduction to the structures of hardwoods and softwoods and their effects on the drying process.
After explaining these factors a number of pages of the notes describe the best practices
to produce dry wood by air seasoning in timber yards and in drying kilns. An introduction
to air seasoning of wood is given, where the expected rates of drying and the limitations
of air seasoning in producing dry wood are described, and the optimal layout of a
timber drying yard is described -
There follows a description of the theory of the kiln drying of wood, where the need to provide a sequence of optimal temperatures, relative humidities and air circulation rates is described and the concept of a “Kiln Schedule” is explained. Different types of kiln drying equipment are described. There follows a comparison of the advantages and disadvantages of using air seasoning and kiln drying to dry wood.
The use dehumidification to dry wood is also described as are high temperature drying and the use of solar kilns to dry wood.
The notes end with descriptions of the various defects in sawn timber which can arise when wood is dried and how these defects can be avoided. The various defects arising in the anisotropic nature of wood are described (spring, twist and checking, for example) as is the serious defect of case hardening of timber. The final page of these notes explains how case hardening of timber can be avoided and mention is made of a number of other defects which can arise when producing dry wood.
Reasons to Dry Timber: An Introduction to Timber Drying
Timber Drying -
Factors controlling the Drying of Wood
The Structures of Softwoods and Hardwoods and their effect on Wood Drying
An Introduction to the Air Seasoning of Timber
Layout of a Timber Drying Yard
Design of Stacks in the Timber Drying Yard
Types of Kiln Drying Equipment
Benefits of Kiln Dried Timber production compared to Air Seasoning Timber
Using a Dehumidifier to Dry Wood
High Temperature Timber Drying
Avoiding Case Hardening by Monitoring the Drying of Timber. Also Collapse & Staining of Timber