If you are dismantling an old deck made of pressure treated decking, you have to dispose of the wood carefully. Wood treated with arsenic, for example, should not be burned, and it shouldn't be thrown in a landfill without permission either. Luckily, there are landfills that have special places to bury pressure treated decking, and there are facilities who can safely burn this type of old decking. Alternatively, however, you can also reuse the decking.
21 September 2015