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ACQ Fence Posts

ACQ is a water-based wood preservative that prevents decay from fungi and insects (i.e., it is a fungicide and insecticide). Water-based preservatives like ACQ leave a dry, paintable surface.

Alkaline copper quaternary

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 the more chemically harmful Chromated copper arsenate (CCA). 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.

Common Uses

Since fence posts will have to go below the ground and thus become exposed to insects and moisture, a treated product is highly recommended. We recommend ACQ for it's rot and insect resistance as well as it's les harmful water based preservative. We recommend 4x4, 4x6 or 6x6 posts for all fence posts.


Adjust post depth for desired post height.ACQ Fence Posts are treated for direct ground contact, however we do recommend that a few steps are taken to ensure your project lasts for years.

Dig post holes approximately 30" deep, and fill with approximately 6" of aggregate (rock) fill for drainage. This will leave you with 24" of post below ground, with a typical 8' post your 6' fence will match right to the top so consider adjusting the depth or buying 10' posts for design style if you prefer the post above the fence top.

Place the post in the hole and fill with cement (preferably) or with soil and pack to firm up the post. While installing, you may need to brace the post to prevent it from leaning before the cement has setup.