What is H3 treated pine?

What building and DIY projects should you use H3 treated pine for?

With so many different types of softwood and hardwood, treated and untreated, it can be difficult to know the difference between all of them.

This article will provide you with everything you need to know about H3 treated pine to help you decide whether it’s right for your project or not.

What is H3 treated pine?

H3 treated pine is timber that has been treated to make it resistant to termites and fungal decay. It is produced by forcing a chemical preservative into the wood.

H3 is treated with a Alkaline copper quaternary (ACQ) which contains copper and quaternary ammonium compounds that protect against deterioration caused by fungi or insects such as borers and termites.

H3 treated pine is suitable for outdoor use, but for above-ground applications only.

What are timber hazard levels?

A Hazard level classification determines what level of protection timber has 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.

What is H3 timber used for?

Most people buy H3 treated pine to build a deck or fence.

The timber is commonly used for the following purposes:

  • Flooring
  • Framing
  • Cladding
  • Fascia
  • Pergolas
  • Window Joinery
  • Weatherboards
  • Decks (above ground only)
  • Fences (above ground only)
Treated pine timber 8 | Building & Landscaping Materials

Is H3 treated pine waterproof?

H3 treated pine is suitable for outdoor use and periodic wetting.

The chemicals in the treatment process protect H3 wood from termite attack and fungal decay, so you can use it for above-ground building projects.

Can you use H3 treated pine in the ground?

H3 treated pine is not protected against severe decay which can occur in continuously damp conditions. It is therefore only suitable for use in conditions where the wood is above ground.

Treated pine timber 9 | Building & Landscaping Materials

In comparison, H4 treated pine has been tested to have resistance to decay when constantly kept wet or used in the ground.

What is the difference between H3 and H4 treated pine?

H3 treated pine is suitable for outdoor use above the ground, whereas H4 treated pine is suitable for outdoor use both above and in-ground.

What does this mean? It means that if you want to use your H3 timber in a deck or a pergola, you can! (but not for the in-ground sections). But if you want to build a retaining wall, H4 is better suited.

How to tell if pine is treated

It’s often important to determine whether your timber has been treated.

This information can be found in a variety of ways, but the most common is through a tag, stamp or brand on one or more sides of the wood.

Treated pine is often easy to spot because it has a greenish tinge compared to untreated timber.

If you are unsure about whether the timber has been treated or not, err on the side of caution and don’t burn it or use it for purposes where it may not be suitable.

What is treated pine treated with?

There are a number of chemicals used in treating timber and the chemical varies depending on what type of treatment you want to achieve.

Boron is one chemical used for treatment. It helps protect timber against termites and other insects. Boron can also be used as a flame retardant, making it perfect as a structural material in buildings that’ll be exposed to fire or high heat, like brick homes.

Synthetic pyrethroids are another commonly used chemical in treated pine products. It acts as a great insecticide and fungicide for timber which needs protection from rot or pests.

Imidacloprid was originally developed for use in pesticides but has since been applied as an agricultural wood preservative.

ACQ (alkaline copper quaternary) is another popular preservative option with low toxicity to humans.

CA (copper azole) type A uses copper compounds combined with boric acid or similar azoles such as tebuconazole, propiconazole or imidacloprid instead of arsenic compounds like CCA does.

CCA (chromated copper arsenate) was once widely used in Australia. It is still used for some purposes and restricted for others due to human health concerns.


Can you use H3 timber inside?

H3 treated pine can be used inside, so long as it is not for food preparation surfaces.

What treated pine does Bunnings sell?

Bunnings offers a range of treated pine products, including their popular MGP10 H2 Blue Pine. Bunnings also sells both stained and unstained treated pine decking, which can be used in outdoor applications where it will be exposed to all types of weather conditions.

Photo of author

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.


Leave a Comment