Cracking and splitting timber
Cracking and Splitting of Timber is a complete pain for our industry during the summer. It’s at this point we get customers questioning the ‘quality’ of our timber used in some of our products as some cracks and splits start to appear in items that use posts such as play equipment and gazebos.
Thankfully, it’s not just us either, every single supplier of timber products for the garden gets exactly the same thing.
Summer historically costs the timber industry thousands upon thousands of pounds due to perceived ‘defects’ in timber by customers when 99% of the time no defect exists at all.
Natural organic substance
Timber is a natural substance, we all know that. As a living organism, it is influenced heavily by its surroundings. More specifically it is trying to reach an equilibrium with it’s natural surroundings.
Water content
When a tree is first cut down (green wood) it can contain over 50% of it’s weight in water. This water is naturally contained in the wood and is divided into two categories:
Free Water and Bound Water.
Free Water is water that is held within the wood via capillary action. It can be absorbed and expelled.
Bound water is water within the wood that is bonded via hydrogen atoms.
When timber is dried it will be the free water that is the first to leave.
Before timber is used it is dried when most of the free water is removed (fibre Saturation Point of Wood (FSP)) FSP is achieved at about 25 – 30% moisture content. Wood is dried to it’s natural surrounding environment and as such is engineered to work within it to about 20 – 25%.
Benefits of dried timber
Decay organisms generally cannot thrive in wood with a low moisture content. Many wood loving insects can only live in green timber.
Dried wood has better thermal and insulation properties.
Preservatives and finishes penetrate better with dried wood.
Dried wood is generally a lot stronger than green wood.
Equilibrium of the environment
As I’ve mentioned wood wants to be the same as it’s environment both in moisture content and temperature. This is where we start to see a problem, especially during the Summer months and soaring temperatures. The timber starts to exhibit cracks and splits where it further dries out from it’s original point of FSP.
It is, by its nature trying to reach an equilibrium with it’s surrounding air moisture. During summer this moisture content in the air is going up and down all the time as is the temperature and the wood is trying to do the same thing.
Seasonal wood shrinkage
Regardless of how well dried a piece of wood is it will always grow and shrink according seasonal changes in relative humidity of the air.
Any change in ambient humidity will affect timber regardless of any other factors.
A good treatment can slow this process down greatly regulating how fast moisture gets in and out of the timber. Wood shrinks by different amounts in different directions, there is however very little movement in the grain lengthwise. There is some shrinkage radially and a greater amount tangentially (along the curvature of the growth rings).
Here’s a picture of my gate post at home, the weather we’ve been having is having a major impact on it. You’ll notice that cracks and splits are appearing and will continue to do so at different rates. Most of the splits are occurring perpendicular to the growth rings because there is more shrinkage along the direction of the rings. At the moment this piece of timber is still drying to reach an equilibrium with it’s surroundings, the inner core is wetter than the outer but once that has dried to the level of the atmosphere virtually all these splits will dissapear.
Examples of timber cracking
Here’s another basic but extreme example. Because of the different rates of radial and tangential shrinkage, distortion of the wood can occur. It can also cause radial cracks from the centre of the wood to the outer edge. This is because the circumference shrinks more than it’s radius and a big radial crack appears allowing the circumference to shorten.
Here’s my post again showing a crack top to bottom, this is a radial split as above and will close up once the whole of the post has reached an equilibrium either by further drying or expansion as the moisture in the air increases such as Autumnal weather.
Here’s another example, this is a crack that’s just starting to emerge, they can appear very quickly during a hot day and often after installation if exposed in the hot sun or stored in a hot environment such as a garage.
The same thing happens to furniture when out in the sun or a change of humidity. This is the timber from my picnic table I photographed yesterday, you’ll notice small cracks are just starting to appear.
Round poles such as the type used in many play centres, swings and climbing frames also exhibit the same properties and often far worse:
What is mainly affected?
The properties exhibited here are mainly found in products that utilise posts such as our gazebos and outdoor play equipment.
Due to the fact that the posts are made from whole tree trunks, this is the case. You can see that very clearly with my fence post as an example, this was not supplied via Tuindeco but by a local fence supplier, our posts however will be the same. This post has been in the ground for about 12 months and supports a gate. This post is encompassing both the ‘Heart’ and the ‘Pith’ of the tree and as such it shrinks and swells at different rates. A whole tree trunk is used as it is considerably stronger than the outside of the tree, If we were to use the outside then we would lose a huge amount of strength, the strongest part of a tree of course is the heart.
As I’ve said and we all know, wood is an organic substance. It also tries its hardest to match it’s environment which you may not know.
It moves, swells, and shrinks to do so and is normal timber behaviour.
This should be fully understood and expected when buying any timber product for your garden. Sometimes these cracks can open up alarmingly large but remember it is entirely normal and once the inner core has dried the crack will close up. Likewise as the moisture in the air increases so will the free water absorbed by capillary action in the wood and once again the cracks will close up.
None of these splits or cracks in the timber will affect it’s structural integrity or inherent strength.
If however, it concerns you I recommend the use of a good quality timber treatment as this will restrict the moisture both entering and leaving the wood.
Basically timber can be viewed as a bit of a pain!
Customers sort through the DIY shops, they buy gazebos or other ‘post’ style products and immediately reject them as being defective, this is simply not true!
Wood, by definition cannot be defective, there is nothing to go wrong other than obvious rot which is very rare in graded timber.
If you experience cracks and splits in your timber, especially when it is obviously milled from a whole trunk it is not a ‘defective’ product, nor is the strength impaired, it simply is timber exhibiting it’s normal state and characteristics.
If you don’t like it, treat it with a good timber treatment and restrict the flow of moisture in and out. However! Even the best treatments allow moisture transfer, even plastic does to a certain extent.
Update: 11th August 2013
I’m going to try and prove my own waffle, I’m going to focus on my fence post, bear in mind it’s been in the ground for about a year and I’m now going to try and study it.
I plan to photograph it over the weeks, months and maybe years ahead. It’s all very well me spouting on about the theory. Some may even see it as excuses for a dodgy bit of timber so lets actually see what happens with this post over time if at the end I’m a liar I apologise. This is going to be interesting ….. as far as a bit of wood can be …
I’m also going to find a brand new post from one of our Gazebos, stick it in the ground and see what that does as well, for now, my fence post …..
-August 5th, split fence post
Updated picture, today, 11th August 2013
Some of the radial lines looks smaller to me, or am I just imagining them? The split at almost 12 o’clock is smaller.
There’s changes but nothing has really closed up.
The week’s weather has had some rain, a couple of storms but not massive amounts, it’s still been pretty warm. Lets see what the next week or two does to it.
The next time I’ll keep the camera back like the picture above so we can really see the changes ….. if any … or at least compare them better.
Update 29-10-13
A huge change since the last time I looked at the post. You can really see the change this time and most of the splits have closed up. Both the heart and the pith are reaching an equilibrium. Clever stuff wood!
Timber splits in construction
I enjoy looking at the properties of timber, it fascinates me how it moves twists and turns yet remains the exact same strength.
On a recent trip to a city shopping center it tickled me to see this split in a main supporting post.
-Crack in supporting post
-A crack big enough for my daughter to put her fingers in!
Amazing stuff timber! This isn’t defective. It’s not a problem and its strength is not at all affected. I hope not, as it’s supporting a massive canopy in the cities new shopping centre!
Update, 11.10.2018
One of our employees had recently returned from a long weekend away in a log cabin – Lucky for some, I know. Although the Log Cabin she has stayed in is seen as a ‘traditional‘ log cabin, meaning that they mostly use rounded/half round logs in their construction, the timber is similar. Just like almost every type of timber you’ll find, there will be cracks and split, but it hardly affected its use for our employee’s holiday!
She writes as follows:
“So thought this might be of interest, I stayed in a pine log cabin over the weekend and you should have seen some of the splits in most of the logs… I’ve attached some pics, it was interesting to see. (The pics aren’t great, sorry).”
I think that the pictures show more than enough to prove that even with cracks the log cabin is still standing strong. It is more than suitable for the accomodation purpose it provides!
About the author: Richard
Meet Richard, a dedicated professional with a rich history at Tuin, contributing 25 years of experience within the garden timber industry. With an expertise in garden buildings. From design, manufacturing and installation for a range of timber buildings. Sheds to log cabins and all the way up to timber framed houses. In his time he had worked with experts all over europe, and also included his own personal experience of installing and testing Garden Buildings from a range of companies, models and sizes. You will find a majority of his blogs to include expert installation advice for your Log Cabin. Information on how timber reacts to different environments and the best way to preserve your garden buildings.
