Alex from New Leaf Landscapes contacted us recently looking for advice regarding using recycled plastic and composite decking. We thought that other readers might be interested in reading our reply and benefitting from our experience gathered over more than 20 years in the business:
The material we supply is all made from 100% recycled HDPE (mainly derived from a mixture of milk flagons and other scrap bottles and agricultural and other industrial waste. The composite decking you refer to is made by blending a range of polymers, including wood mill flour, rice waste, aggregate dust and fibreglass. These give different properties to the material, in the case of the vegetable derived composites it generally makes a wider range of colours available, while in the case of the fibreglass composites it improves the stiffness. At present we do not stock these composite products. We are looking at the fibreglass composite for a specific range of applications where the improved stiffness would be a real advantage. In the past we have found that vegetable derived composites (especially the numerous products from the far east) tend to absorb moisture and can then behave unpredictably and potentially can be damaged by frosts.
The recycled plastic planks we supply are very tough and sturdy and will obviously not rot, or be affected by frost. However, it does have properties which make it different from timber which do need to incorporated into any design – people sometimes get unstuck when they simply replace timber with a similarly sized plastic component. There are two issues which need to be considered.
1. Thermal expansion – generally the coefficient of thermal expansion for HDPE is about 1mm / meter / 0C. This is quite a bit more than you would expect with timber, or indeed most other materials. The specific remedies to be born in mind are that sufficient expansion gaps are allowed for. Gaps of a couple of mm between planks laid widthways are sufficient. Along the length, a gap of about 6mm per meter should be allowed for and if possible oversized holes should be used to allow the material. This can mean that long runs of material (4.8m lengths etc) can be unworkable and smaller planks with expansion gaps built in work more successfully. In practice, this is often not done with large structures, open structures where the material can all move relatively freely (walkways, dipping platforms etc) and it often does not create serious problems, but where used on a design with tight specifications (a deck in a sunny courtyard between walls for example) more care needs to be taken.
2. Flexibility – you infer that this is a consequence of the thermal expansion, and while it certainly does get more flexible when it gets hot it is always more flexible than timber – a lot of the flexural strength of timber is derived from the bundles of fibres which make it up. In comparison recycled HDPE is a more uniform material, and is also inherently flexible. This means that thicker planks are often needed and a more substantial substructure is required. I would normally recommend bearers at every 500mm and maximum post centres of 1.5m, but these will depend on the specific profile and design used.
I hope I have not put you off too much!!! The consequence of the thicker planks and the additional substructure are that the material can work out more expensive than an equivalent tanalised softwood structure. However, besides the lack of any maintenance requirements and other benefits such as lack of splinters, ultimately it pays for itself by not having to be replaced, which is why it is requested by so many architects and specifiers today. The potential issues are only problems if they are not considered during the design stage. One compromise which may marry the best of both worlds is the use of timber decking on a recycled plastic substructure. You can read about the experience of one of our customers (who used a completely recycled plastic deck) here:
http://www.filcris.co.uk/pdf/Pumphrey%20Decking.pdf
If you have any other queries do not hesitate to get in touch, similarly if you would like samples of our products we are very happy to send them. We will be at the Creating Landscapes Show at Capel Manor in October if you would like to see the product in the flesh and talk to us face to face.
Chris Went
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