Grey Deck Cleaner
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Deck Care

Grey Deck Cleaner

Oxalic acid crystals that take the grey out of weathered timber and bring back the look of new wood — the prep step that decides how the oil goes on afterwards.

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1 kg tub Schedule 6 — POISON under the Poisons Standard (oxalic acid)

↓ Safety Data Sheet ↓ Technical Data Sheet

Does: Strips grey and black weathering; lifts tannin and rust stains
Use on: Weathered exterior timber before oiling, and nearby concrete
Format: Oxalic acid crystals. 1 kg makes 10 L.
Not for: Spraying. Bare metal or glass.

Need advice? Call 03 9532 0679.

Directions for use

Preparing the timber, then applying

Before you start

Gloves, eye protection, cover upThe crystals and the solution are corrosive to skin and eyes. Wear gloves and protective clothing for the whole job.
Wet the gardenPre-wet nearby foliage so run-off is diluted, and rinse it again when you finish.
Knock off the worst firstHeavy blackening comes off faster with a stiff brush or a high-pressure washer before the acid goes on.

Cleaning the timber

Read the pack and the Safety Data Sheet before use.

Dissolve 1 kg in 10 L of hot waterA 10 % solution. Mix in a plastic bucket.
Work it inWork the solution into the timber with a stiff deck brush. Do not spray it — the mist is a severe respiratory irritant.
Rinse thoroughlyWash the timber down thoroughly with water. Stubborn areas get a second application, then wash down again.
Dry, then oilAllow the timber to dry thoroughly before sealing it — with Aussie Clear, Exterior Pine Clear or the finish of your choice — to stop it greying again.

Application rate

Mix and coverage.

Item	Rate
Dilution	1 kg crystals to 10 L hot water (10 %)
Coverage	Approximately 50 m² per 1 kg tub
Stubborn stains	Second application, then rinse

Safety & hazards

Safety directions and first aid

Safety directions

The crystals are corrosive to the skin and eyes. Wear gloves when handling the crystals and the diluted solution. Avoid contact with skin. Do not spray the solution — the spray mist is a severe irritant to the respiratory tract.

First aid

Wash contaminated skin with plenty of water. Irrigate eyes with copious quantities of water for at least 15 minutes. If ingested, give water to drink. Do not induce vomiting. Seek immediate medical assistance and contact a doctor or the Poisons Information Centre (13 11 26).

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

Where it goes

Grey, black or stained timber

Any exterior timber that has gone grey or black from weathering, before it is oiled or coated — and the concrete around it.

Weathered decksThe standard first step before re-oiling.

Grey fences & screensBack to the colour of new wood.

Cedar weatherboardsEspecially useful on blackened Western Red Cedar.

Tannin bleedDark streaks from hardwood tannins.

Old linseed oil finishesMay need vigorous scrubbing to lift the discolouration.

Concrete & pavingRust spots, tannin drips and light oil stains on driveways and paths.

Plants and metalPre-wet nearby foliage and rinse it afterwards. Keep the solution off bare metal and glass, and never mix it with other cleaners — it reacts explosively with strong oxidising agents.

Reverses the weathering

Why it works

Grey timber is dead surface fibre and dirt, often with black mould staining through it. Oxalic acid dissolves the grey layer, lifts the black staining and opens the grain — so the timber underneath looks like new wood and takes oil properly.

Takes out the grey

Cleans grey or blackened timber caused by weathering — decks, fences and especially Western Red Cedar weatherboards.

Lifts tannin and rust

Removes tannin bleed from natural timber, and rust spots and tannin drips from concrete and masonry.

Fresh every time

Supplied as crystals, not a pre-mixed liquid, so the solution you scrub with is at full strength.

Technical data

Specifications

Active constituents

100 % oxalic acid, transparent white crystals.

What it does

Not a preservative. Cleans grey and blackened timber, removes surface mould staining and lifts tannin and rust stains; oil the timber afterwards to stop it greying again.

Rate, coverage & reapplication

1 kg dissolved in 10 L of hot water (a 10 % solution) cleans approximately 50 m².

Pack sizes

1 kg tub. Also 25 kg bags for trade.

Poison schedule

Schedule 6 — POISON under the Poisons Standard (oxalic acid). Not an APVMA-registered product; the schedule applies to the chemical, not to a pesticide label.

Storage & shelf life

Store in a cool, dry place out of direct sunlight, away from oxidising agents and foodstuffs. Reacts explosively with strong oxidising materials.

Common questions

Do I have to use it before oiling a grey deck?

Yes, if you want the oil to work. Oil over grey fibre sits on dead wood and looks patchy. Clean first, let it dry thoroughly, then oil — the timber takes it evenly and holds it longer.

Why crystals instead of a liquid cleaner?

A pre-mixed liquid weakens on the shelf. Crystals dissolve to a full-strength 10 % solution at the moment you need it.

Is it safe for the garden?

Diluted correctly and rinsed, yes — pre-wet nearby plants before you start and rinse them again after, so run-off is diluted.

Can I spray it on?

No. Brush it in with a stiff deck brush. The spray mist is a severe irritant to the respiratory tract.

You might also need

Aussie Clear

What goes on after — the penetrating oil for hardwood decks.

View product

Exterior Pine Clear

What goes on after a treated-pine deck.

View product

D-Mould

When the problem is mould and algae rather than grey.

View product

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