Alternative copper based timber treatments to copper chrome arsenate

The two main copper based timber treatments, other than copper chrome arsenate (CCA), are alkaline copper quaternary (ACQ) and copper azole (CA). Both are less hazardous to the environment and human health than CCA.

timber used in the garden

Copper azole sleepers used as a bush walkway

ACQ is a water-based timber treatment that uses copper to protect timber from fungi and a quaternary compound to protect timber from copper resistant fungi and insects. It is applied by vacuum pressure impregnation. ACQ is also called ammoniacal copper quaternary or amine copper quaternary.

CA uses copper in the same way as ACQ, with the addition of the fungicide, tebuconazole.

Hazard level of timber treated with alkaline copper quaternary and copper azole: H3 to H5.

Pests repelled by alkaline copper quaternary and copper azole repel: Moderate to very severe decay, borers and termites.

Typical uses of alkaline copper quaternary and copper azole

Both ACQ and CA can be used outside, in and above the ground, and in fresh water. Both ACQ and CA are suitable for

  • exterior flooring, framing, cladding and decking
  • fascia, pergolas and fence posts
  • retaining walls and handrails
  • outdoor equipment and garden furniture
  • building poles

Safe handling: See Working with and handling treated timber safely

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