If you’re buying a timber product to be located outside, whether it’s fencing, a garden shed or an arbour, then Andy Hobson says that you need to know about how the timber is treated and the difference between pressure and dip treatment.
Treating wood is very important, as over time timber will become increasingly susceptible to rot and insect attack which can severely damage it.
Dip treated products are generally cheaper than pressure treated equivalents as the process of dip treating takes less time, leading to lower labour and storage costs.
However, the treatment will thin and fade over time and most manufacturers recommend annual repeat treatments to comply with their guarantee conditions. They will also advise that you isolate a dip treated product from the ground using a pressure treated gravel board.
Although they are cheaper to buy, you need to weigh up what is important to you, whether you want to save money initially or to spend more time and money treating the product annually.
The process of pressure treating, or vacuum pressure impregnation as it is officially known as, involves a longer process. Firstly the wood is dried naturally using air flow or a kiln, this removes moisture from the wood so it is ready to be treated.
Next the wood is placed into a pressure treatment tank, and air is removed via a vacuum. Then the tank will be flooded with preservative liquid, and finally the excess fluid is extracted using a vacuum again.
The low pressure of the wood draws the preservative deep into the grain of the wood making for a fully treated piece of timber.
Pressure treated products can usually be identified by their green tinge finish when new, but this will fade to a honey brown colour over time, naturally blending into your garden.
Weathering will not affect pressure treatment, so it will last much longer. Although if you do saw/cut a piece of pressure treated timber manufacturers will always advise to treat the newly exposed part.
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