ACQ
Alkaline Copper Quaternary, an arsenic-free water-borne preservative used for H3 and H4 timber where human contact or environmental sensitivity rules out CCA.
Alkaline Copper Quaternary is a water-borne preservative combining copper as a fungicide with quaternary ammonium compounds (quats) for additional fungal and insect protection. It contains no arsenic or chromium, making it the common choice for residential decking, handrails, balustrades, garden furniture, and playground timber where human contact is expected. ACQ retentions for H3 and H4 hazard classes are defined in AS/NZS 1604.1. The treatment leaves a green-brown tint that fades with weathering. For buyers, ACQ is more corrosive to ferrous fixings than CCA, so use Type 304 or 316 stainless steel or hot-dip galvanised connectors as recommended by AS 3566 to avoid premature fastener failure. Always seal cut ends with a compatible preservative.
Values and references on this page are indicative and drawn from common industry sources. Always verify the current AS/NZS standard, manufacturer data sheet or NIAA policy publication before relying on figures for design, specification or compliance work.
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