Cracking and Splitting in Timber
Cracking and Splitting in Timber
(Taken from Richards blog at www.tuin.co.uk)
Timber – A bit of a pain
Summer in general is a complete pain for our industry, 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. And, as it is organic, it is greatly influenced by its surroundings and more specifically it is trying to reach equilibrium with its natural surroundings.
When a tree is first cut down (green wood) it can contain over 50% of its 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 its 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 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 its 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 its original point of FSP.
It is, by its nature trying to reach equilibrium with its 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.
A change in ambient humidity is all that is needed and will always affect timber regardless of any other influences.
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).
What is mainly affected?
The properties exhibited here are mainly found in products that utilise posts such as our gazebos and outdoor play equipment.
This is because the posts are made from a whole tree trunk.
As I’ve said and we all know, wood is an organic substance. It also tries its hardest to match its 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 its 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, and 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 its normal state and characteristics.
Enjoy it and embrace it as it is part of its charm and warmth we all enjoy. Watch it and marvel at its behaviour, cracks and splits will disappear, open up, wander and move …. Is it really a pain or a bloomin’ clever feature of a very basic material we all love? 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.
The ONLY thing to remove the transfer of moisture is aluminium as found in crisp packets! Cover your posts in this and they will never crack or split.