Treated Pine vs Hardwood Decking

Treated pine decking and hardwood decking are both common in Adelaide backyards, and the choice between them is usually about budget, durability and looks. Pine is a softwood that needs chemical treatment to survive outdoors. Hardwoods such as spotted gum, blackbutt and merbau are naturally durable and far harder.

Below we explain how each one works, what the treatment codes on pine actually mean, and where each timber makes sense.

Pine vs hardwood deck: the key differences

Hardwood is harder, naturally durable and richer in colour, while treated pine is lighter, softer and generally the more budget-friendly decking timber. The table sums it up using published WoodSolutions data.

Factor	Treated pine (radiata)	Hardwood (e.g. spotted gum)
How it resists rot and termites	Preservative treatment	Natural durability of the heartwood
Natural durability (untreated)	Class 4, non-durable	Spotted gum is Class 1, very durable above ground
Treatment class for decking	H3 (outside, above ground)	Not needed for durable heartwood
Seasoned density	About 550 kg/m³	About 990 kg/m³ (spotted gum)
Janka hardness (seasoned)	About 3.3 kN	10.1 kN (spotted gum)
Resistance to dents and wear	Lower, marks more easily	High
Appearance	Pale with knots, often stained or painted	Natural tones from pale to deep red-brown
Movement and splitting	More prone to cupping and splitting if left uncoated	Generally more stable, still needs coating to limit checking
Typical use	Budget decks, deck frames, painted decks	Feature decks, high-traffic decks, pool surrounds

Hardness figures are measured on the Janka scale, which tests how much force it takes to press a steel ball into the wood. The higher the number, the better the timber resists dents from furniture, heels and pets.

What H3 and H4 mean for treated pine

H3 and H4 are hazard classes under the Australian standard for preservative-treated timber (AS/NZS 1604). The class tells you where the timber can safely be used.

H3: outside, above ground. WoodSolutions describes H3 as timber exposed to periodic wetting and leaching that is able to dry out between wettings, with decay and insects as the main threats. Decking boards, joists, cladding and fascia boards fall here.

H4: outside, in ground. H4 is for timber in the ground or continuously damp, where the risk of decay and termites is severe. Posts set in the ground and landscaping timbers are typical H4 uses. WoodSolutions notes that H4 is not intended for critical structural elements; those need a higher class or a durable Class 1 hardwood.

Treated timber is branded or labelled with its hazard class, so check the label rather than relying on colour. In practice, a well-built deck might use:

• H3 treated pine joists and bearers
• Stumps or posts suited to in-ground exposure, such as H4 treated timber or steel, depending on the design
• Hardwood, composite or H3 pine boards on top

One rule that is easy to miss: cut ends, drill holes and notches in treated timber need to be re-coated on site with a suitable preservative. Treatment does not always go right through the board, so a fresh cut can expose untreated wood.

Why hardwood does not need treatment

Durable hardwoods rely on the natural chemistry of their heartwood to resist decay and termites. WoodSolutions explains that the heartwood of dense hardwoods such as spotted gum and blackbutt does not absorb preservatives well, so their natural durability is what you rely on.

The Australian natural durability classes run from Class 1 (very durable) to Class 4 (non-durable). Untreated radiata pine is Class 4, which is why it must be treated for outdoor use. Spotted gum is Class 1 above ground and blackbutt is Class 2. Sapwood, the outer band of the log, is less durable in all species, which is why good decking boards are selected for heartwood or have any sapwood treated.

For a closer look at the main hardwood species, see our guide to spotted gum vs merbau decking.

Treated pine decking: pros and cons

Treated pine is a practical, lower-cost timber, but it asks more of you in maintenance and wears faster underfoot.

Pros:

• Generally the more budget-friendly decking timber
• Light and easy to work, which can help on simple, low decks
• Takes paint and stain well if you want a coloured deck
• Plantation grown and widely available

Cons:

• Soft, so it dents and scratches more easily under furniture and heavy use
• More prone to splitting, cupping and raised grain if not kept coated
• Knots and a paler look that some people find less appealing
• Needs care with cut ends during construction

Hardwood decking: pros and cons

Hardwood decking costs more up front but gives a harder-wearing, better-looking deck that suits heavy use.

Pros:

• Very hard, so it resists dents, wear and pet claws
• Naturally durable heartwood, with some species rated Class 1 above ground
• Rich natural colour and grain
• Some species are suited to bushfire-prone areas when boards are thick enough. Check the species and your site’s BAL.

Cons:

• Higher material cost
• Harder to work, with pre-drilling needed for fixings
• New boards release tannins that can stain nearby paving until they weather
• Still needs regular oiling to hold its colour

Which decking timber suits your deck?

Choose hardwood for decks that see heavy use, sit around pools or are a feature of the home. Treated pine can make sense for budget decks, painted finishes or a deck frame under better boards.

Situation	Our usual suggestion
Main entertaining deck off the living area	Hardwood or composite boards
Pool surround	Hardwood or composite, chosen for comfort and slip resistance
Low-traffic side deck or garden platform	Treated pine can be a sensible budget choice
Deck you plan to paint	Treated pine
Deck frame under any boards	H3 treated pine or steel, with in-ground parts suited to H4 or similar
Bushfire-prone site	A suitable hardwood or tested product, subject to your BAL

If neither timber appeals, composite boards are another option. Our guide to composite vs timber decking explains the trade-offs.

Adelaide conditions to keep in mind

Adelaide’s hot, dry summers are tough on timber surfaces. Strong sun dries out uncoated boards, which can lead to checking and splitting, especially in softer pine. Winter rain then soaks in, so good drainage and ventilation underneath matter for both timbers.

On reactive clay soils found in parts of Adelaide, footings need to be designed for ground movement, whichever boards go on top. Sloping blocks in the foothills often mean taller decks with more framing, where the choice of frame material becomes as important as the boards.

Maintenance compared

Both timbers need cleaning and recoating, but pine tends to need more attention to stay in good shape.

1. Sweep regularly so debris does not trap moisture.
2. Clean with a deck cleaner a few times a year.
3. Recoat when water stops beading on the surface. Many owners recoat about once a year, more often on decks in full sun. Check the product’s guidance.
4. On pine, keep an eye out for splits, lifting nail heads and soft spots near the ground.

Our step-by-step guides on how to oil a deck and deck cleaning and maintenance cover the details.

Your next step

If you are deciding between treated pine decking and hardwood, we can walk your site, look at how the deck will be used and price both options so you can compare. See our timber decking page and our overview of decking in Adelaide for more on how we build. Call us on 0485 008 292 or use the quote form, and we will get back to you within 24–48 hours.