Traditional Oak Frame Buildings

What you need to know about looking after, and/or finishing your oak framed building. (And oak furniture, doors etc.!)

A little bit of oak history...

Oak (or 'genus quercus' in Latin) is a hardwood with around 600 known species. The oak tree is native to the Northern Hemisphere and includes deciduous and evergreen species extending from cool temperate to tropical latitudes in the Americas, Asia, Europe, and North Africa. North America contains the largest number of oak species, with roughly 90 in the U.S, while Mexico has 160 species of which 109 are endemic. The second largest collection of oak varieties is China, which comprises approximately 100 species.

It has always been a popular wood in the UK, used to build navy ships in the 18th century, paneling in the Houses of Parliament, and the very heart of Westminster Hall. It is the "Tree of Britain". Wander round many British towns and cities and look up above the shop fronts! It was the core of our homes, amazing architecture, build grand halls to basic homes. Our countryside would not be British, if it didn't have oak trees on its landscapes and horizons. In more recent times, it has seen a resurgence, and has become more fashionable in construction again.

The flowers of many oak trees are known as catkins and they are produced by oaks when they reach their reproductive age, which is usually 20. They are generated by rising temperatures in spring. Ultimately it is the catkins of many oaks that turn into the acorns. Hence the old fashioned and popular phrase... "from mighty oaks little acorns grow".

How to treat your oak

With regards to finishing and treating oak there are plentiful options, but there are frequently asked questions. Commonly, we are asked how external oak can be kept looking natural, when the build is finished. Whilst the question is easy, the answer is not so. These are the essential considerations :-

• When water penetrates oak, it reacts with the tannin naturally in oak, resulting in 'blackening'.
• The sun's UV rays turn the oak to a silvery grey over time.
• Clear products are inevitably not completely clear so they tend to 'bring out' the natural colours of the oak, making it darker and a warm golden colour.
• The wind, rain and sun will make a difference to how quickly the oak changes colour.

If the desire is to keep the oak looking as natural as possible, but to prevent blackening or silvering as much as possible, then the following is the best method 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 contains biocide which is important for external oak, 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 desire is to protect the oak whilst maintaining the silvery appearance then the following is the best :-

• 1 coat of clear wood preservative
• Followed by 3-5 coats of Tung oil

Tung oil is one of the clearest oils on the market and doesn't give UV protection.

If you want the exterior oak to be coloured, then the following method is advised :-

• 1 coat of clear wood preservative
• followed by 1 coat of your chosen colour of Osmo natural oil wood stain
• followed by 1 coat of Osmo UV Protection Oil 420 Extra

If blackening on exterior oak needs removing then a wash with a fungicidal wash is suggested. If you wish to remove the silvering, a scrub with Osmo wood reviver, or an Oxalic acid is recommended. The crystal form is better, which dissolves in warm water. It is important to follow the instructions and advice from the manufacturer when using this. It is advised to have a practice with the Oxalic acid first, before attempting your frame.

Another common enquiry we get is how to keep internal oak looking natural. You cannot just apply "clear products", as this will bring out the natural colours of the wood, and make it darker and more golden. A good way to see how your oak will look once it has been finished with a "clear" coat is to apply water to an offcut. The look when the wood is wet is very close to how it will look with a clear varnish or oil applied.

Some clients like the way oak colours when clear coatings are applied, while others want it to look as natural as possible. This natural look can almost be achieved by adding some white to your chosen top coat, but a test on an offcut is a MUST, because each wood needs a different mix of clear top coat to white.
Here are some guidelines :-

• If an oiled finish is preferred, then apply two thin coats of Hard Wax Oil Natural or Polyx Oil Raw.
• Alternatively, you could make your own mix, using white hard wax oil with 2 parts of the clear hard wax oil.
• If a varnished finish is favoured, then 1-part white dye can be mixed with 50 parts clear varnish.

Clear wax polish is the one exclusion to the above... If a clear wax polish is applied to bare oak, then the colour is kept very natural indeed, the only question is whether a wax polish is going to be durable enough. Internal doors are considered ideal for finishing with a wax, but a floor may look nice when waxed, but regular upkeep is needed, so most people don't go for that.

If the desire is for the oak to be made darker, then hard wax oil is perfect, because it colours and protects the wood in one go. It's a good to finish with a clear coat, because if the wood gets scratched, then it is the clear coat that scratches first, and not the coloured coat, hence the scratch wood not be noticeable.

Oiling consideration
If oak is being oiled then it is best to sand it with a sandpaper that is no finer than 150 grit. This opens the pores of the wood, and allows the oil to penetrate the wood better, giving a greater protection.