There are a number of difficulties in working with oak that others have developed through trial and error that can be invaluable. Understanding the challenges of working with hardwoods can save time, energy and money and avoid a satisfying, constructive project becoming a chore. The physical properties of oak have made it a perfect choice for external use, construction and furniture for centuries. Oak is solid, hardwearing and lasts seemingly forever, it is extraordinarily resistant to water damage and pests and needs little or no maintenance. However, the very same properties that make it such a desirable material can make it difficult to work with. Understanding the physical makeup of the timber itself and which cuts are most appropriate for the job in hand pays dividends.
Use the Right Variety
Most British users will automatically opt for European oak, it is the most widely available type after all. This is no accident, European oak is easily procured and suited best to the British climate, particularly for external applications. Many online articles on oak woodworking by American authors reference white or red oak. While red oak has its own distinct look and any piece using it will create a talking point, it is far less durable. Red oak has more open grains, giving it a porous texture that significantly lowers its water resistance. This makes it unsuitable for any outdoor projects and even for others it will need treatment. European oak also has a proven chain of custody to guarantee ethical production
Understand Green vs. Dried Oak
As oak timber dries the moisture that keeps it relatively soft is lost and it becomes harder and more difficult to work with. For this reason if you are planning to work extensively on the timber, green oak is probably the best choice. Green oak is also the cheapest option and, as it requires no processing, the most environmentally friendly choice. If used outdoors, green oak will change colour, silvering over time in response to the elements. As a result, the wood will need to be treated with preservative to retain the original colour if this is desired. Green oak will also shrink over time and if it is used for cladding or flooring, this will need to be taken into account to avoid unsightly gaps.
For renovation projects where the existing timber is already aged, air dried or kiln dried oak will usually be a better choice. It will already have a ‘pre-aged’ look more consistent with the existing woodwork. Due to the lower moisture content (20% – 30% for air dried, 8% – 10% for kiln dried) it will be harder and more difficult to work with. Before drying the timber will be cut to specific lengths, so finding larger sizes may be difficult, if not impossible. Drying also takes time, so if supplies run out they can be difficult to replace without a considerable wait.
Fixtures and Fittings
Traditionally oak structures have used tenon and mortise joints or wooden pegs have been used to connect individual parts. This was mainly due to the cost of metal components or a lack of availability, especially in rural locations. For the modern user, there is no shortage of metal fastenings, but care must be taken in which is used. Iron based metals are best avoided as the tannins in the oak can react with the iron causing blue or black staining. In green oak the higher water content can cause iron to rust, weakening the joint. Not only will the metal become corroded and weak but the wood in contact with it can suffer a loss of tensile strength as well. (http://www.vam.ac.uk/content/journals/conservation-journal/issue-04/corrosion-of-metals-associated-with-wood/). These stains can only be removed by bleaching agents such as oxalic acid, but many are corrosive and toxic. Brass, aluminium or copper are far more suitable options, but while brass fittings complement the colour of oak, they can be prone to shearing. Dried oak pegs will form a stronger joint over time as the oak shrinks around them, gripping them tightly. They will also give a more consistent, uniform finish as they blend in with the surrounding wood. If glues are used, care must be taken as water based glues can cause swelling and warping in dried oak as they transfer moisture back into the timber.
Keep Your Tools Sharp
With any hardwood and especially oak, sharp tools are an absolute must. The cells of the wood are packed tighter with few air spaces in between them and higher attractive forces binding them together. As a result, chisels and planes will have a far tougher time parting the grain without the sharpest edge. Using force to drive in a dull edge will result in splitting rather than cutting, damaging the wood beyond repair. Planning without a sharp edge will lead to the plane skating over the surface rather than shaving it. Attempting to adjust depth and push harder will only make the job harder, shaving more wood away with a blade less suited to the work. Oak is also susceptible to burning from the friction of blunt power tool attachments. Not only will this leave burn marks requiring intensive sanding to remove, it can damage blades and bits. In some cases this can cause the metal to lose its temper so even when sharpened it will not hold an edge for as long. Using sharp blades and bits and operating power tools at the correct speed should avoid this. Finally, when working with green oak, all tools should be cleaned and dried afterwards, as the moisture and tannins can cause corrosion.
Where possible, use quarter sawn timber if you will be planning it yourself. With oak this is not difficult as the size of the original tree means much of the timber derived will be quarter sawn. The wider edges will be cut across the radial plane, that is, across the growth rings. The weaker bonds along the radial plane mean far less effort is needed during planning. Planning the narrow edges will be harder, but the smaller width means less work is needed and the trade off is well worth it. Obviously, the timber merchant will be able to plane timber before purchase, but plans can change mid project and this will save work in this event.
Make sure the length and width of any timber purchased is correct before beginning work. This may seem obvious, but if bulk buying it is easily overlooked and can lead to unnecessary hard work.
If planning the ends of boards is necessary, wetting the ends will allow the timber to absorb moisture and soften slightly. Alcohol is often recommended for this, but it can evaporate before the work is finished. Apply water or mineral spirits liberally and leave for a couple of minutes to absorb and soften the wood. Linseed oil works even better if it is available.
Cutting mortises or dovetails can be incredibly time consuming and tiring if only using a chisel on oak. Try using a coping or turning saw to cut to the baseline of the gap between dovetails, then use a sharp chisel to tidy up and finish the gap. To cut out mortises, use a brace and bit or power drill (at appropriate speed) to bore out most of the waste, then finish and tidy up with a chisel.
Oak has particularly heavy graining and this can cause problems when routing, splitting or chipping at the ends if it is done too aggressively. Rather than attempting to rout the surface in one pass, use two or three passes with less force. This should give a neater, consistent result needing no further work.
Hardwoods Group are established wholesale suppliers of green, air dried and kiln dried oak with a wide range in stock at all times. For any trade enquiries or advice on which is most suitable for your current project, , we will be happy to help.
Working With Green Oak
Air Dried Vs. Kiln Dried Oak
Properties of Oak Wood