Using fresh sawn or seasoned timber can make or break the success of street furniture on a project; specifying the wrong option could result in a warped wall top seat which affects the structural stability of the surrounding planter, or a design may be created that is impossible to build due to unavailability of timber in the required sizes. Therefore, it is important to consider the options when specifying timber, particularly Oak, on a project.
What is Fresh Sawn?
Also known as: Green Timber, Green Lumber
Fresh sawn, or green timber, refers to timber that has been recently felled. The crucial thing to understand is that the moisture content will be much higher than Air Dried or Kiln Dried. For example, the moisture content of green Oak is approximately 80%.
What is Seasoned Timber?
Also known as: Wood Drying, Air Dried Timber, Kiln Dried Timber, Dehumidified
Seasoning is the generic name of the process that reduces moisture content of fresh sawn timber. Timber that has been through the seasoning process is known as seasoned.
Seasoning is usually done by air drying or kiln drying – both methods are slightly different. Air drying is the more traditional method which involves simply leaving the timber in a dry place to dry, usually over the course of years. Kiln drying is a newer method and involves applying heat to dry the timber which is a much faster process, typically weeks. However, this the methods are irrelevant for this article because the result for both methods is to achieve timber with a moisture content of around 10% – 20%.
Fresh Sawn Advantages
Fresh Sawn Disadvantages
At the heart of the debate between using fresh sawn or seasoned is if you place higher value on availability or stability. If you need availability particularly in unusual sizes, then fresh sawn is likely to be your best option. However, if you need the timber to be stable and not move, then seasoned is probably more suited to you. Despite this, for external furniture, the answer is very subjective and heavily dependent on the species of the timber and size. Some suggestions below:
1, Iroko and Opepe are not badly affected by movement and warping, therefore more suitable to use as fresh sawn timber. This is because species with a close grain are less likely to move. The grains of these species are closer than almost any other species in the world.
2, Heartwood will not warp as much as sapwood. For more information on these terms, please read this blog.
4, It is unnecessary (and impossible) to use seasoned Oak with a cross sectional area of greater than 150mm.
5, Conversely, it is absolutely recommended to use seasoned Oak if the thickness is less than 80mm.