Heavy Oil Preservative
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Timber Protection

Heavy Oil Preservative

The heavy-duty copper preservative. A heavier oil carrier stays on the surface as a film — more waterproof and longer-lasting than a standard preservative, built for trade and structural timber.

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500 mL, 2 L, 4 L, 10 L, 20 L and 200 L Schedule 5 — CAUTION APVMA 60813

↓ Safety Data Sheet

Protects against: Fungal decay and some species of woodborer
Use on: Above-ground timber — end grain, joints, deck subframes
Format: Heavy copper oil. Brush or roller, two flood coats.
Not for: Ground contact: use In-Ground Paste. Water-based paint over it.

Not sure it's the right product? Compare preservatives or call 03 9532 0679.

Directions for use

Preparing the timber, then applying — as per the approved label

Structural or load-bearing timber? Veranda posts, bearers, joists, rafters: get a qualified professional to decide whether it can be treated or needs replacing. Preservative stops decay spreading; it can't restore lost strength.

Before you brush

Remove decayed timber firstFor remedial treatment it's essential to remove all decayed timber from the surface before applying — a preservative protects sound wood, it doesn't rebuild it.
Clean weathered timberOn decks and weatherboards, use a wood cleaner to remove the grey from the surface before treating.

Dark green now, brown laterHeavy Oil goes on dark green and browns off with weathering — quickly on most timbers, more slowly on light timbers like pine.

Stays oily · not where people touchThe surface can feel oily afterwards, so avoid it where timber comes into direct contact with clothing — handrails, seating, pool decks. For frequent-contact timber, Timber Preserver is the better choice.

Applying the oil

Always read the label before use.

Flood on two coatsApply liberally by brush or roller to the areas needing protection — especially end grain and exposed surfaces. Best results come from two flood coats.
Allow absorption between coatsIn cooler conditions the oil takes longer to absorb, so allow more time between coats.
Leave natural, or oil-based paint onlyWater-based paints are not recommended over Heavy Oil. Leave it to weather, or use oil-based finishes.

Application rate

Per coat, on prepared timber.

Rate	Coverage
1 litre per coat	6–8 m²

Two flood coats. Protection period about 2–3 years. Clean brushes with mineral turpentine.

CAUTION · As per the approved label

Safety & hazards

Signal word, restraints and first aid — from the approved label

As per the approved label. Always read the label before use.

Schedule 5 — CAUTION

May irritate eyes and skin. Do not inhale vapour; ensure ventilation.

May irritate the eyes and skin. Avoid contact with eyes and skin. Do NOT inhale vapour. Ensure adequate ventilation during use. Wash hands after use.

First aid

If poisoning occurs, contact a Doctor or Poisons Information Centre (13 11 26). If swallowed, do NOT induce vomiting — give a glass of water.

Full safety directions and first aid are on the product label and the Safety Data Sheet.

Handling & environment

Preschem handling guidance — general advice, not label text. The approved label and the Safety Data Sheet take precedence.

Handling

Oil resistant gloves should be worn when using the product. Excessive contact with the product can cause dryness and mild irritation to the skin. Similarly eye protection should be used when working overhead or with spray guns. Wash hands with soap and water after use.

Environment

Avoid contamination of waterways and sewers as the product will form an oil pollution hazard.

Where it goes

Above-ground structural timber, especially where you can't re-treat later

For hardwood and softwood in above-ground situations — particularly end grain, joints and surfaces with restricted ventilation. Recommended especially for deck subframes and timber that's hard to get back to.

Deck joists & bearersThe subframe under the boards — the label's headline recommendation, and the "can't re-oil later" case.

Posts & sleepersAbove-ground structural and landscape timber.

Wharves & bridgesHeavy-duty above-ground structural timber exposed to weather and damp.

Hardwood retaining wallsLandscape timber holding back soil, treated above the groundline.

Decking & weatherboardsExposed exterior surfaces — a natural-look preservative that weathers to brown.

Pergolas & exposed jointsEnd grain and connection points where boards meet bearers — the classic decay spots.

A heavier oil with built-in water repellency

Why it works

Same proven copper naphthenate as our standard preservative, but carried in a heavier oil that stays on the timber surface as a film rather than soaking away — so it repels water, holds its protection longer, and is built for structural and trade work.

Heavier, longer-lasting

The heavy oil carrier stays on the surface and keeps repelling water — more durable protection than a lighter, faster-absorbing preservative.

Set and forget

Ideal where ongoing oiling isn't achievable — deck subframes, bearers and structural timber you can't easily get back to.

Decay & borer protection

Protects above-ground timber against the fungal decay that exposure and damp cause, and some species of woodborer. Weathers dark green to brown.

Technical data

Specifications

Active constituents

20 g/L copper (Cu) present as copper naphthenate · solvent 930 g/L hydrocarbon liquid.

Rate, coverage & reapplication

6–8 m²/L per coat, two flood coats. Protection period about 2–3 years. Clean up with mineral turpentine.

Pack sizes

Available in 500 mL, 2 L, 4 L, 10 L, 20 L and 200 L.

Poison schedule

Schedule 5 — CAUTION. May irritate eyes and skin. Do not inhale vapour; ensure ventilation.

APVMA registration

APVMA 60813. Distributed by Thomson White Australia.

Storage & shelf life

Store in the closed, original container in a dry, cool, well-ventilated area, out of direct sunlight.

Common questions

How is this different from Timber Preserver?

Same copper naphthenate active — the difference is the carrier. Timber Preserver uses a lighter hydrocarbon that absorbs into the timber; Heavy Oil uses a heavier oil that stays on the surface as a film, so it's more waterproof and lasts longer. Heavy Oil is the trade and structural choice; Timber Preserver is the lighter everyday one.

Will it change the timber's colour?

Yes. It goes on dark green and browns off as it weathers — quickly on most timbers, more slowly on light timbers like pine. If you need no colour change at all, Clear Wood Preservative is the zinc-based alternative.

Can I paint over it?

Only with oil-based finishes. Water-based paints are not recommended over Heavy Oil. Most people leave it to weather naturally.

Can I use it on handrails or seating?

It's not the best choice there. The surface stays slightly oily, so it can mark clothing — avoid handrails, seating and pool decks. Clear Wood Preservative is the better option for timber people touch often.

You might also need

Clear Wood Preservative

The clear alternative — no green tint, safe for frequent-contact timber like handrails and furniture.

View product

In-Ground Paste

For the groundline — where timber meets soil, below where Heavy Oil's above-ground use ends.

View product

Australian made in Cheltenham, Victoria since 1988 — founded by two CSIRO timber scientists. The whole story →