Alkaline copper quaternary

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Alkaline Copper Quaternary (also known as ACQ) is a water based wood preservative method recently introduced in countries where there is a demand for alternatives to Chromated copper arsenate (CCA).[1] The treatment is made up of copper, a bactericide and fungicide which makes the wood resistant to biological attack, and a quaternary ammonium compound (quat) which acts as biocide, increasing the tolerance of treated timber to copper-resistant bacteria and fungi, and also acting as an insecticide.

ACQ has come into wide use in the USA, Canada, Europe, Japan and Australia following restrictions on CCA, as ACQ is seen as a "greener" preservative and a more sustainable option. Its use is governed by national and international standards which determine the volume of preservative uptake required for a specific timber end use. It is applied by industrial vacuum-pressure impregnation at a timber treatment plant.

As it is an alternative to CCA, ACQ can be used for wood with low to extremely high exposure to the elements and weathering. The concentrations used increase with the corresponding expected levels of exposure of the timber. The treatment lends a distinctive green tint to the timber, although pigment can be introduced during the treatment process to stain the wood in shades of brown and green. ACQ-treated timber can be painted, but this is not necessary.

In the US and other countries, ACQ is registered for use on: lumber, timbers, landscape ties, fence posts, building and utility poles, land, freshwater and marine pilings, sea walls, decking, wood shingles, and other wood structures.[2]

All ACQ treatments accelerate corrosion of metal fasteners relative to untreated wood. Hot-dipped galvanized, copper or stainless steel fasteners must be used.[3]

Chemical Specialties, Inc (CSI, now Viance) received U.S. Environmental Protection Agency's Presidential Green Chemistry Challenge Award in 2002 for commercial introduction of ACQ. The widespread use of this wood preservative in some countries has eliminated the requirement for the arsenic and chromium contained in CCA.

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