What is ACQ treated pine?

And how does it differ from other treatment methods such as CCA?

When it comes to the wood you use in projects, you want to get it right the first time.

In this post, we will cover all you need to know about ACQ treated pine.

What is ACQ treated pine?

Treated timber 2 | Building & Landscaping Materials

ACQ is a water-based treatment that protects timber from the effects of weather, rot, and insects.

According to The NSW Environment Protection Authority, ACQ “uses copper to protect timber from fungi and a quaternary compound to protect timber from copper resistant fungi and insects.”

They say it “can be used outside, in and above the ground, and in fresh water” and that typical uses include “exterior flooring, framing, cladding and decking, fascia, pergolas and fence posts, retaining, walls and handrails, outdoor equipment and garden furniture, and building poles”.

Hazard level classification

All ACQ treated pine should have a Hazard level classification which determines its level of protection against certain exposures.

These range from H1 – H6, as displayed in the table below.

Timber Hazard level table | Building & Landscaping Materials
This table showing timber hazard level and treatment types has been reproduced with permission of the NSW Environment Protection Authority.

The following Hazard levels are treated using ACQ:

What does ACQ treated mean?

ACQ stands for Alkaline Copper Quaternary and is a water-based solution of copper, chromium and quaternary ammonium compounds.

It is applied by vacuum pressure impregnation, or VPI, which simply means that the treatments are forced into the timber.

It has been used as an alternative to CCA treated pine since around 2004.

CCA vs ACQ treated timber: what’s the difference?

CCA treated timber was the standard timber treatment until around 2003. ACQ is now more commonly used.

Both types of treatment are similarly effective in protecting the timber from insects and decay.

The main difference between them is their toxicity; CCA has been banned in many countries due to environmental concerns as it contains arsenic, a known carcinogen.

The NSW Environment Protection Authority says that ACQ is “less hazardous to the environment and human health than CCA.”

Instead of using arsenic, ACQ uses another compound called quat (or quaternary ammonia), which is less toxic.

This is an important factor for people who plan to use treated pine for their home DIY projects.

Is ACQ treated pine safe for vegetable gardens?

Many people prefer not to use CCA treated pine (which contains arsenic) for vegetable gardens. However, CSIRO does assign a tolerable risk, based on their research.

ACQ treated timber is generally considered to be safer to use than CCA as it does not contain arsenic.

However, as discussed in this report by Pennsylvania State University “ACQ contains more copper than CCA, and some copper will leach from ACQ-treated lumber as it does from CCA-treated lumber.”

If you are concerned, you can line your vegetable garden with plastic or another material to prevent leaching.

You could also use untreated hardwood sleepers as an alternative to treated pine.

Keep in mind that root vegetables are more at risk of absorbing toxins from the soil than those that grow above ground.


How long does ACQ treated pine last?

ACQ treated timber lasts a lot longer than most untreated timber. The life span of ACQ treated pine will depend on the conditions the timber is exposed to. However, in many cases, you can expect ACQ treated timber to last for 100+ years.

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Steve Kropp

Based in Melbourne, Steve's passion is vegetable gardening, and he’s been writing about it for almost 5 years. He also loves all things DIY and is always looking for a new project. When not working on his own garden projects or blogging, Steve enjoys spending time with his family, cooking meals with produce harvested from his garden, and coaching his son’s footy team.


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