What Everyone Should Know About Finishing Oak

Welcome to part 2 of our series on wood types. This week I’ll be discussing oak & oak wood treatments. If you haven’t already read part 1, feel free to go check it out here: All about Pine Wood.

A Little History of Oak

Oak (or quercus as it is known in Latin) is a hardwood with some 400 known species. It has always been a popular wood in the UK, but in recent times it is even more widely used in construction and also as internal fixtures in clubs and gyms etc. For furniture construction, oak has become ever more the wood of choice, a trend expanding year on year since the year 2000 when China, India and Indonesia substantially increased their export markets. Pine has been the wood to suffer from oak’s popularity as it is more widely available in the Far East.

The flowers of many oak trees are known as catkins and they are produced by oaks when they reach their reproductive age, which is typically around 20 years. They are triggered by rising temperatures in spring. Ultimately it is the catkins of many oaks that turn into the acorns, so maybe that popular phrase… ‘mighty oaks from little acorns grow’ should be ‘mighty oaks from little catkins grow’, although it doesn’t quite have the same ring, does it?

Acorn of the mighty oak tree.

Treating Oak Wood

With regard to finishing and treating oak, there are numerous possibilities, but there are certain requirements that are asked for time and again… Often we are asked how external oak can be kept looking natural. Whilst the question is easy, the answer is not so straightforward. These are the necessary considerations:

• When water penetrates oak, it reacts with the high tannin content within oak, resulting in ‘blackening’.
• The sun’s UV rays will turn the oak to a silvery hue over time.
• Clear products are inevitably not completely clear, so they tend to ‘bring out’ the natural colours of the oak, normally making it a bit darker and warmer.
• The levels of rain, wind and sun will make a difference to how quickly the oak changes colour.

Oak turned grey/silver by UV rays & water damage.

Oak barrels traditionally used for whisky and beer.

If the requirement is to keep the oak looking as natural as possible, whilst preventing blackening or silvering as much as possible, then the following is the best system we know of:

• 1 coat of clear wood preservative
• Followed by 2 coats of Osmo UV Protection Oil 420 Extra

Osmo 420 Extra offers UV resistance and also contains biocide which is important for external timbers as it prevents the wood from becoming diseased with wet rot, dry rot and blue stone etc. The oil also repels water, thus preventing it from going black.

If the requirement is to protect the oak whilst keeping the silvery appearance, then the following is the best:

• 1 coat of clear wood preservative
• Followed by 3–5 coats of high-quality tung oil such as Morrells Tung Oil

Tung oil is one of the clearest oils on the market and doesn’t offer UV resistance.

If the exterior oak needs to be coloured, then the following system is recommended:

• 1 coat of clear wood preservative
• Followed by 1 coat of your chosen colour of Osmo Natural Oil Woodstain
• Followed by 1 coat of clear Osmo UV Protection Oil 420 Extra

If blackening on exterior oak needs removing, then scrubbing with a fungicidal wash such as Barrettine Mould and Mildew Cleaner is recommended. On the other hand, it may be the silvering that needs removing. If so, a scrub with Osmo Wood Reviver Gel (which contains oxalic acid, amongst other active ingredients) is recommended.

Unfinished oak.

Treated oak.

One of the most common enquiries we get is how to keep internal oak looking natural. This is not just a case of simply applying ‘clear products’ as they bring out the natural colours of the wood, thus making it a little darker and more golden. A very good indication of how your oak will look once it has been finished with a ‘clear’ coat is to dampen an area by applying some water with a clean cloth or sponge. The look achieved when the wood is damp/wet is very close to how it will look once a clear varnish or a clear oil has been applied.

Some customers like the way oak colours when clear coatings are applied to it, whilst others want it to be as close as possible to how it looks in its natural state. A more natural look can be achieved by using wood oils that have been specifically formulated to retain the natural appearance of interior oak. These products include:

• If an oiled finish is preferred, then apply two thin coats of Fiddes Hard Wax Oil Natural or Osmo Polyx Oil Raw.
• If a varnished finish is preferred, then 1 part Manns Classic Wood Dye can be mixed with 50 parts Manns Extra Tough Interior Varnish.

Clear wax polish is the one exception to the above… If a clear wax polish is applied to bare oak (or just about any other wood for that matter), then the colour is kept very natural indeed. It’s just a question of whether a wax polish is going to be durable enough. Internal doors, for example, are considered, by most people, to be ideal for finishing with wax, whereas a floor will look nice once waxed but regular maintenance is required, so most people don’t opt for wax for this reason.

If the oak needs to be made darker, then Osmo Polyx Oil Tints or Fiddes Hard Wax Oil Tints are ideal because they colour and protect the wood in the same application. It is always good to try and finish with a clear coat if possible because if the wood gets scratched, it is the clear coat that scratches before the coloured coat and therefore the scratch is not as noticeable.

Oiling Consideration

If oak is being oiled, it is a good idea to sand it with sandpaper that is no finer than 150 grit. The reason for this is that the pores of the wood are more open, thus allowing the oil to sink into the wood better. Better absorption equals greater protection.

Interesting Oak Stats

• Oak bark is rich in tannin and is used by tanners for tanning leather.
• Acorns can be used for making flour or they can be roasted for making acorn coffee.
• Tannin dissolves and escapes from the wood. Wine barrels are made from oak and it is the tannin that helps to give the wine its colour.
• Sessile oaks of Europe can reach heights of up to 40 metres.
• Oak trees regularly live to be 500 years old, although 1,000-year-old oaks are also known.
• A mature oak tree can produce up to 50,000 acorns!

Need help finishing a project made with oak?

For more help and advice on how best to finish oak, contact our team of resident experts who are always on hand to help with project advice and product recommendations.

We love to see before, during and after photos of any wood finishing project. If you would like to share your project pictures with us and our followers, you can either send us some photos or share on our Facebook, Twitter, Pinterest or Instagram pages.

Other great oak-related blogs to consider

• Oak Floor Maintenance – Top Tips for Finishing Oak