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Builder Eric's tips on Expansion and Contraction

When speaking to customers, highlighting the benefit of a good treatment is something we always do. It is a small cost compared to cost of the timber building, but repeatedly, customers choose a poor quality product. No wonder they get in touch the next year to point out cracks or uneven, shrunken logs. Unfortunately, this is fully related to the poor treatment that has been used and is difficult to fix. This could be a poor quality treatment or one that it has not been allowed to penetrate deeply into the wood or has virtually washed off in the first spell of rain.

A simple truth - wood is a product that absorbs. It is a natural product that moves and warps in various ways, which is one thing. However it also has the properties of a sponge and absorbs moisture to a high level. Think of your own log cabin as a moisture absorbing entity. If you think of every log in your log cabin as an individual sponge, that is a good place to start. All logs within your cabin whether long or short, all act this way. Exactly the same, the doors and window frames act in the same way too. Every time there is humidity in the air, whether it is damp or raining, they are absorbing.

Humidity across the UK

The relative humidity or current level of moisture in the air has a direct link to the moisture contact of the wood within it. A wooden building in Swansea on a damp day or a wooden building in Kent where on a dry day, are both adapting to their own individual surroundings. Outside humidity and the moisture level of wood is fully connected and relates directly to each other. In the UK, as an average, we have a high humidity of 92% and a low of 69%. It does depend which part of the country- some parts will never get as high as 92% and some will never get as low as 69% but it is an average and as a worldwide comparison, it is quite high.

With an outdoor building, the variation in this humidity might be seen in several ways. That might be as gaps appearing between smaller and larger logs. The surface area of a smaller log is obviously smaller overall and will shrink quicker than a big log. We use logs with an optimum moisture level at around 14%. However we can still see some issues occur. When the humidity in the air drops below 75%, logs will follow that pattern and lose their moisture too. Imagine if you have a situation where you have not treated your logs at all or have only used a minimal amount of poor quality treatment. It is hardly surprising that your logs could shrink quite rapidly. Those smaller logs could lose their moisture and create gaps in your walls.

This can be hard to imagine, but see it as a sponge. You have large and small sponge layers. Squeeze all the small sponges. When you hold them tight with the water squeezed out, they are smaller. It is exactly the same for the logs. When you see it like that, it follows that moisture levels go up and down over time. A customer once let us know that they had difficulty building their cabin. Their logs were tight and difficult yet the neighbour‘s cabin that come from another supplier had been very easy. It is now simple to see why. Build it in late autumn when it is very humid versus early summer and the logs will be more solid and less loose. If you started with a log that has an 18% moisture content rather than one with 12% it can be easy to see how the variation happened. You can also see that it was perfectly natural and not actually a problem at all.

Therefore it is easy to see that during a long hot summer, the moisture content in some logs can fall as low as 10%. You can probably guess exactly what will happen – plenty of overdry logs that have become so loose. Our aim is for a great fit for your log cabin and a moisture level of 14 – 16% within the wood. Add a deeply penetrating high quality treatment to this for a lower variation in the moisture content. It will give a much longer lifespan and make all the difference to a product you can be happy with, and proud of, for years. Love your wood and do it proud.

Got a question? Get in touch with Eric: [email protected]  

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