The science behind weathering: How larch and oak age over time

As natural construction materials go, it does not get much better than timber. This renewable resource brings qualities to your project that man-made alternatives just cannot replicate, including its unique ability to weather beautifully. For many architects and homeowners, this evolving appearance is part of the appeal, lending rustic charm and plenty of character to cladding, fencing and decking projects.

But how do timber species such as Oak and Larch weather, and what is the science behind their silvery-grey? Let’s take a closer look.

What is Timber Weathering?

Weathering refers to the process in which the colour of your timber changes when it is exposed to sunlight and rain. Typically, your timber will transform from its original hue into a charming silvery-grey, with a slightly darker grain running through the wood. This does not affect the structural integrity of your timber and can be prevented with protective treatments, but there are plenty of designers and architects out there who specifically order weathered timber for its rustic-chic aesthetic.

The Science Behind Timber Weathering

The change in timber’s colour occurs as a result of chemical reactions within the structure of the wood itself. These are triggered by the timber’s exposure to sun, rain and oxygen.

First, let’s take a look at ultraviolet (UV) light from the sun. UV rays begin breaking down lignin, which is the natural polymer which gives wood much of its rigidity and its colouring. As lignin degrades, rain washes it away from the surface. What is left behind are exposed cellulose fibres, which appear much paler and eventually take on the familiar silver-grey tone associated with weathered timber.

This process happens on the very top layer of the wood, which is why weathering affects appearance without necessarily affecting performance.

Next up is moisture. Rain and humidity draw out extractives, which are organic compounds unique to each timber species. These extractives influence everything from colour to scent to natural durability. As they leach out, they subtly shift the timber’s hue, and in some cases can cause streaking or patchiness in the early stages of weathering.

Then there is oxygen. When timber reacts with air, oxidation alters the colour within the wood fibres. In hardwoods such as Oak, this reaction often deepens the tone before greying takes over, giving the wood a rich transitional colour. Softwoods, e.g. Larch, typically move through a lighter, more uniform transition to silvery-grey.

Together, these reactions create the unique patina which so many designers love. They also explain why different timbers weather at different speeds and in different ways.

How Oak and Larch Age Over Time

There are a whole range of factors affecting the timber species you choose for your project. If weathering is important to your construction’s final aesthetic, this is likely to be a big consideration, so we thought we would take a quick look at how two of the most in-demand timbers for weathering compare:

• Oak: Thanks to its high tannin content, oak often darkens or develops streaks in the early stages as tannins react with rain and oxygen. Over time, this deepening gives way to a refined silver-grey patina. Dense and slow to erode, Oak tends to weather evenly, creating a sophisticated, timeless appearance which suits both heritage and contemporary designs.
• Larch: Initially warm and golden, larch gradually softens as UV exposure breaks down surface lignin, moving quickly toward a pale, silvery tone. Because larch contains fewer tannins than Oak, its transition is cleaner and more uniform, though subtle variations in grain can still add character.

For both Larch and Oak, it all depends on the condition and level of exposure, but as a rough guide, you can expect to wait for upwards of 1-2 years for your timber to transition fully to a silvery-grey, although the process begins from day one. Don’t want to wait that long? Look for alternatives, such as ThermoWood which tends to weather slightly faster, or consider coating your timber in a silver-grey stain.

Whatever your desire, speak to our experts at Ecochoice about all your timber cladding options.