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Grey Deck Cleaner
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.

  • Oxalic acid crystals
  • 1 kg makes 10 L
  • Strips the grey
  • Before you oil
  • Corrosive — wear gloves

Where to get it

Find a stockist
Pack sizes
1 kg tub
Poison schedule
Schedule 6 — POISON under the Poisons Standard (oxalic acid)
Australian Made certified Australian made in Cheltenham, Victoria — since 1988

Need advice?
03 9532 0679

Directions for use

Preparing the timber, then applying

Before you start

  1. PPE Gloves, eye protection, cover up The crystals and the solution are corrosive to skin and eyes. Wear gloves and protective clothing for the whole job.
  2. PLANT Wet the garden Pre-wet nearby foliage so run-off is diluted, and rinse it again when you finish.
  3. BLACK Knock off the worst first Heavy 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.

  1. MIX Dissolve 1 kg in 10 L of hot water A 10 % solution. Mix in a plastic bucket.
  2. SCRUB Work it in Work the solution into the timber with a stiff deck brush. Do not spray it — the mist is a severe respiratory irritant.
  3. RINSE Rinse thoroughly Wash the timber down thoroughly with water. Stubborn areas get a second application, then wash down again.
  4. DRY Dry, then oil Allow 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.

ItemRate
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 pack 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 decks The standard first step before re-oiling.
Grey fences & screens Back to the colour of new wood.
Cedar weatherboards Especially useful on blackened Western Red Cedar.
Tannin bleed Dark streaks from hardwood tannins.
Old linseed oil finishes May need vigorous scrubbing to lift the discolouration.
Concrete & paving Rust spots, tannin drips and light oil stains on driveways and paths.
Plants and metal Pre-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, usually with mould in it. Oxalic acid dissolves the grey layer, kills the mould, 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.
Protects against
Not a preservative. Cleans grey and blackened timber, kills surface mould 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.
Before you start

Worth reading first

Deck care Restoring a grey, weathered deck Read more → Deck care Oiling a deck — preparation and timing Read more →
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What goes on after — the penetrating oil for hardwood decks.

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Exterior Pine Clear

Exterior Pine Clear

What goes on after a treated-pine deck.

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D-Mould

D-Mould

When the problem is mould and algae rather than grey.

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