What’s the difference between green oak and oak?
Firstly, we need to identify what forms of oak there are and why they’re different. Timber is a natural porous material and will absorb and lose moisture throughout its lifespan, once it’s cut from the tree this process still occurs but will overtime begin to lose more water than it absorbs.
This ‘raw’ form of timber is known as green oak or fresh sawn oak and will often be used in construction projects or structural supports. This is because fresh sawn is the point in its lifecycle where it will be at its easiest to work with when it comes to sawing and fabrication. It is also the time where it will be at its most economical cost.
Of all the hardwoods available, fresh sawn green oak strikes a perfect balance between quality and economy and its natural resilience to all environmental damage is one of the best, which makes it ideal for self-contained structures such as pergolas and gazebos.
Green oak, like any timber, will begin to dry out overtime and lose moisture. This is part of a process known as ‘moisture movement’. Moisture movement is where the timber will swell and expand with water absorption and shrink with water secretion.
This process is expected and necessary when considering the application of the timber in construction and joinery. When using timber indoors, the goal is to reduce the moisture content to a manageable enough level, so it doesn’t shrink much further and affect the aesthetic or structure of the timber.
What is green oak? How is it different to air dried?
As explained previously overtime green oak will dry without human interaction regardless and after a few years will lose enough moisture to be deemed air-dried. Air-dried is a point at which the timber will have done most if not all its natural drying and won’t reduce any further.
In green oak specifically, natural air-drying has a very special effect which changes the aesthetic of the pieces entirely. In air-dried oak as it shrinks from moisture loss, the surface begins to split and crack leaving a very distinguished and refined aesthetic.
Surprisingly, this doesn’t diminish structural capabilities. On the contrary, the shrinkage compacts the composition of the oak making it more rigid. This creates a more stable structure when a building is erected from green oak as all the joints are pulled together and tightened up.
Something to bear in mind with air-dried oak is it is much harder than its green fresh sawn counterpart and will likely have a blunting effect on tools.
What type of Oak for woodworking and indoors?
Oak is also very popular in carpentry and joinery thanks to its excellent quality and reasonable price. It must however be dried sufficiently to ensure there is no movement as the last thing you want is for it to expand or shrink, as this will create instability and potentially warp the piece.
Using naturally dried oak would achieve a manageable moisture content but as mentioned above the oak will develop splits, cracks and surface checks which can make the timber too difficult to work around. It will also be air-dried from the surface inward so if you we’re to cut the timber in half, there would still be one green oak face.
This is where human intervention is required and the oak will undergo a process called kiln drying. Kiln drying is a method of drying which will rapidly dry out the oak in a kiln to a point where no more moisture movement will occur.
Due to the quickness that the oak is dried in the kiln, kiln dried oak does not have time to shrink, which bypasses the issues with the splits and cracks when air-dried. Instead, you’re left with a clean finished piece of oak with a low enough moisture content to be suitable in woodworking.
Its always important to get the best material for the job so if you are interested in oak for your project and you are still unsure after reading this article, please get in touch using our online services such as the online chat and email or give the sales team a call.
We’re oak specialists after all and we’ll make sure you get the best advice!