Timber offcuts, sawdust and ash cannot be used for compost. Please do not put them in the organics bin or in your home compost as it may contaminate them.
Ash waste needs to be cooled for at least 5 days before disposal, to ensure there is no risk of embers reigniting. We are working collaborative with the Fire Brigade to raise awareness of this issue, and as a result of bin, house and collection truck fires from ash waste.
If a bin is collected containing ash waste that has not been cooled, it causes a risk to public safety. We have had a number of fires in trucks, and the collection truck driver has had to act quickly to find a safe place to empty the collected waste. This causes not only a public safety issue but also causes delays to traffic and the remaining bin collections in that area.
When you burn treated timber, not only are considerable amounts of toxic heavy metals released into the air we breathe, but the ash waste contains 100 times the concentration of toxic heavy metals than the original piece of timber/wood.
Heavy metals are found naturally in our environment, like in our tree clippings, but can also be concentrated by certain processes.
Timber may be treated which chemical solutions to prolong its life, particularly when used for outdoor and building purposes. It is difficult to identify whether timber has been treated or not, and once it’s in with all the other organics waste, we can’t get it out again – which means any compost we make from it is contaminated, and can’t be used in any soil.
In New Zealand, the following chemicals may have been used to preserve timber:
A kilogram of treated wood can contain over 8,000 times the levels of contamination, and we can’t remove it from the organics waste that goes in the green bin, or the compost that it’s turned into. That’s why we need to think about how we manage timber offcuts, sawdust and ash in our waste, to stop it getting in there in the first place.
As little as a third of an ice cream container of ash can be enough to contaminate the contents of one whole green bin collection truck load of organics waste. Once it’s in there, we can’t get it out, and contaminated compost can’t be added to soil to help grow our food and gardens.