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Know about Wood


Wooden Climbing Frames and Swing Sets: Know about Wood

In recent years timber has become a popular choice for outdoor toys.  For reasons of affordability and the environment, softwood rather than hardwood is used by the majority off wood playset manufacturers.  Over the last few years there has been a move towards wooden playsets being manufactured in China, these play sets use a timber called China Fir, which is from the cedar family.  You can choose between wooden climbing frames and wooden swing sets constructed with round timbers or square cut timbers. When making your choice, you should be aware of the differences between them.


Wood: an organic material 

Each piece of timber is unique, bearing its own knots, cracks and variations in colour.  This is part of its beauty. However, as a natural organic material, it will change over time, as it reacts to variations in atmospheric conditions.  Softwood will expand and contract with fluctuations in temperature and humidity.  In warm, sunny weather timber will shrink.  In wet weather it will expand.  As these physical changes do not take place uniformly throughout the wood, stresses are set up which result in cracks and splits opening up.  These cracks can be both wide and deep and are more likely in round wood than square wood, although they will occur in both.


Round wood: characteristics and maintenance advice

Round timbers from smaller trees contain heartwood surrounded by sapwood .  They are subject to significant cracking.  When you experience cracks and splits on a roundwood timber play frames, it is not a ‘defective’ product, nor is its inherent strength or structural integrity impaired, it is simply exhibiting its normal state and characteristics. Each piece of timber is unique, bearing its own knots, cracks and variations in colour. These characteristics should be fully expected to be present at the time of delivery and continue to develop during the products lifecycle.

Timber is a natural organic substance. And, as it is organic, it is greatly influenced by its surroundings. It moves, swells, and shrinks according to seasonal changes in relative humidity of the air.

Roundwood frames are constructed from timbers that come from younger smaller trees and are complete tree poles, stripped of any bark and other rough materials but subject to no further processing. 

When a full round timber dries, the exterior surface (sapwood) shrinks faster than the inner (heartwood) heart of the timber. Consequently, stresses occur in different directions during drying. This means that the full round timber tends to develop a V-shaped check towards the centre.

Sometimes these cracks can open alarmingly in length and width, but this is entirely normal and once the inner core has dried the crack will close (not disappear). 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.

Both laboratory and field tests prove that the natural cracking and splitting does not materially affect the strength of the timber. The frames are also designed and dimensioned to ensure these natural characteristics do not have an impact upon the structural integrity. 

All of the roundwood timber, we supply, is pressure treated with an environmentally friendly preservative. This is a process that penetrates to the core of the wood, helps withstand the elements and wards off termites, microorganisms and fungal decay. After the treatment process it is normal for a green flecking to become visible on the surface of the wood. 

Performance guarantees do not rely on a periodic application of preservative, although you may wish to do so for aesthetic reasons and to further extend the life of the product.

Because of the natural characteristics of such timber products, it is vital that parents check their play frame regularly to identify any splintering or lifting of the surface layers of the wood or any exposure of rough wood due to changes in cracks and splits. Affected areas must be rubbed down using coarse sandpaper to restore a smooth, safe surface.

There is no necessity to replace timber parts that exhibit cracks and splits. 



Square wood: characteristics and maintenance advice 

Wooden climbing frames and wooden swing sets made from square cut timbers will contain less heartwood than the round timbers.  This will reduce instances of cracking and splitting when compared with round wood but cracks and splits will still occur.  Again, you can be reassured that wood playsets are dimensioned and designed to ensure that this has no effect on their structural integrity.  Just as with round wood, your wooden climbing frame or wooden swing must be regularly checked.  Any areas affected by splintering or lifting should be rubbed down with coarse sandpaper to restore a smooth surface suitable for wood playsets.


Square wood:  pine and china fir

As already mentioned the majority of wooden climbing frames are manufactured using pine.  There are different grades of pine, the better quality grades will have less knots, be less likely to split and the timber will be more dense.  The higher the density, the stronger the timber and the more it weighs giving a more stable product.  Creative Playthings and Playtime Series are both manufactured using a grade 1 southern yellow pine, which is the highest grade.  Tp, Plum Products and All Out Play also use a pine although we do not know which grade.

Climbing frames manufactured in China will use china fir some call this a Cedar because it is from the hard wood family.  This timber is not pressure treated but does have a water repellant stain applied at the point of manufacture.  The china fir is not as dense as pine so will weigh less than pine. Plum Products smaller playsets are made from china fir.