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As I’ve mentioned in previous articles we use a H3 CCA treated pine substructure which the suppliers offer a 50 year guarantee on. In order to activate that guarantee we need to adhere to best practices and there are a few things that we need to do, and document by way of pics.
Although all decks we build are built according to best practices, when applying for a guarantee we need to document it. So if you require a guarantee please let us know beforehand so we can collect all the documents we need to process it. These include charge sheets and retention records from the treatment plant to ensure that the chemicals used in the treatment process penetrated the timber properly. The charge sheets also document all sorts of things such as how much solution was added to the chamber, how much wood was in the chamber and how much solution much was left over. From this one can work out what the penetration was and can be verified through the retention records.
When the wood is treated it is placed in a chamber and all the air is sucked out to create a vacuum. Solution is then added to the chamber which now takes up the void or vacuum and the solution is sucked into the timber. They call this pressure treatment.
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CCA is an abbreviation for Chromated Copper Arsenate. The copper stops fungus growing on the wood, which in turn causes the fibres of the wood to break down and rot. The arsenate stops insects from eating it and the chrome binds the two so that they don’t leach out of the wood. There are different hazard classes of CCA treated timber. For a full explanation you can visit http://www.sawpa.co.za (South African Wood Preservers Association).
Once this pine has been treated it can now get wet without the fear of it rotting because the fungus cannot grow. It is not water that causes rot, but rather fungus. The water allows the fungus to grow which breaks down the fibres of the wood which causes rot. So now your wood can get wet without rotting.
When the wood is treated, this CCA solution they use penetrates the timber based on the pressure they use and the time it remains in the chamber. The longer the time, the greater the pressure and the stronger the solution, the higher the hazard class and more resistant it is to rot and insect infestation. So timber being used outdoors subject to weathering (rain and sun) needs to be of a higher Hazard Class than timber being used in your roof where it is protected from rain to a large degree.
The depth of the penetration is subject to the density of the timber (pine vs. saligna or gum), and the time in the chamber. These retention records mentioned above are obtained from coring a section of the timber on each batch to ensure that the solution penetrated the timber properly. The charge sheets will outline how long the timber was in the chamber, the strength of the solution etc.
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So once all these documents have been collated, one can apply for a guarantee from the suppliers of the solution used in the treatment process.
One last criterion is that where we cut a piece of timber we need to treat the end grain with an end sealer approved by the supplier. This is because the solution used in the treatment process does not penetrate all the way through the timber. Depending on the density of the wood it will penetrate about 16mm into the timber. With pine, as opposed to saligna, it will obviously penetrate further as the timber is softer. Timber such as balau cannot be successfully treated as it is too dense. However it rarely needs to be treated as it is naturally resistant to insect infestation and rot due to the resins and oils naturally found in the wood.
By following the manufacturers and SAWPA’s guidelines one can successfully use treated pine as suitable outdoor timber for decking.
The pictures alongside show where we have used an approved end sealer to treat the timber on all cut ends.
For a free no obligation quote on your decking and other outdoor requirements please contact us on 082 496 5444 or use the contact form below.