Decking normally comes already treated when you buy it, however, what treated is depends, it could be treated by anything varying from coloured dye to high retention tanalizing which is pressure treated to a British Standard, or at least it should be...buyer beware...some timber is treated using what is called the Vac Vac process, that used to use solvents for the treatment and is commonly used for treating timber in manufactured windows etc, not really suitable for ground contact timber, what we call a full Tanalizing process is done with water mixed with various chemicals/salts etc it used to be called CCA as the ingredients were copper/chrome/arsnic, that may have been superceded by now, never the less "Tanalized" timber is good for 25-30 years or longer if the treatment was done correctly and the right species of timber is used, the best timber for Tanalizing is the sapwood of Scots Pine preferably home grown.
If you have access to a local home grown sawmill then you might get a chance to pick the species you are after.
Be warned though, just because the timber looks olive green or brown it does not mean that it has been treated to British Standards, some suppliers use the trick of putting in the pressure tank just long enough for it to take on the colour of the fluid or even worse in an open dipping tank with dye in it, technically it's been "treated" but with what...not good. If you can get your decking from a home grown sawmill you can specify for the timber to be treated twice or to marine standard, this gives in effect double salt retention, pressure treating should be available for around £40/£50 a cubic meter, that's a lot of timber. The timber used must be rot free before it's treated. Decking should not have ground conact, it is important to have a good free flow of air underneath it, any timber support posts should be a minimum of 100 x 100 mm dimension or 150 x 150 mm if you want it to really last.
Hope this is of use to someone.
Lawrence
If you have access to a local home grown sawmill then you might get a chance to pick the species you are after.
Be warned though, just because the timber looks olive green or brown it does not mean that it has been treated to British Standards, some suppliers use the trick of putting in the pressure tank just long enough for it to take on the colour of the fluid or even worse in an open dipping tank with dye in it, technically it's been "treated" but with what...not good. If you can get your decking from a home grown sawmill you can specify for the timber to be treated twice or to marine standard, this gives in effect double salt retention, pressure treating should be available for around £40/£50 a cubic meter, that's a lot of timber. The timber used must be rot free before it's treated. Decking should not have ground conact, it is important to have a good free flow of air underneath it, any timber support posts should be a minimum of 100 x 100 mm dimension or 150 x 150 mm if you want it to really last.
Hope this is of use to someone.
Lawrence
