Consumer advocacy teardown
HG Rust Stain Remover alternative & active ingredient dupe
Stop paying £8.50 for HG. The bulk active is Oxalic acid dihydrate — 86% less per working litre than a typical pack.
- Active
- Oxalic acid
- CAS
- 6153-56-6
- Dupe
- Oxalic acid dihydrate
- Saving
- 86% / L
Saving is per litre of working-strength mix versus a typical pack price, not versus the DIY kit total. Shop prices move — always check the listing.
The Marketing Claim & The Catch
A typical 500 millilitres pack of HG Rust Stain Remover is about £8.50 in patio & exterior. That is a snapshot, not a live Amazon price — listings, sizes and deals move. The marketing line is that you are buying a finished lifestyle product, not a weighed chemical.
On the pack: Removes rust stains from stone, concrete and paving; Also lifts fertiliser and leaf-tannin marks; and Ready to use.
The catch: Oxalic acid is the classic rust and tannin bleach for masonry. HG bottles a dilute solution; a kilogram of crystals makes tens of litres of the same chemistry.
- “Removes rust stains from stone, concrete and paving”
- “Also lifts fertiliser and leaf-tannin marks”
- “Ready to use”
Proprietary Blend & Dosage Breakdown
The labelled active is Oxalic acid at 10%. Everything else in the pack is water.
At 10% active, most of what you pay for is carrier and packaging. The brand is selling convenience, fragrance and a label — not a uniquely potent molecule.
Branded working strength is whatever comes out of the bottle. The bulk alternative is 99% Oxalic acid dihydrate, mixed to 50 g/L.
- Labelled active
- Oxalic acid
- 10%
- Carrier
- Water
- Retail pack
- 500 millilitres · £8.50
The Active Chemical Alternative (Dupe Stack)
The dupe stack is Oxalic acid dihydrate at 99% bulk. Indexed as CAS 6153-56-6, formula C2H2O4·2H2O. Buy it as 1 kg for about £9.99 from Amazon UK.
Working strength: 50 g/L. Indicative cost £0.50 per diluted litre — 86% below a typical branded pack on a per-litre basis, before you reuse leftover bulk.
Follow the mixing method and the supplier SDS. Wear the listed PPE. Do not mix incompatible oxidisers, acids or ammonia.
- Toxic if swallowed; wear gloves and goggles. Keep away from children and pets.
- Dissolve 50 g of crystals per litre of warm water (about 5% w/v) for a patio rust wash.
- Apply, dwell 10–20 minutes, agitate, then rinse thoroughly with plenty of water.
- Do not mix with bleach (toxic gases) or use on marble that you care about — it etches carbonates.
- Store dry. Neutralise spills with bicarbonate, then rinse.
Mixing desk
Dilution calculator
Switch between filling a sprayer and covering a measured surface. Figures are educational estimates from the listed ratio — always check the SDS.
Formula
Oxalic acid dihydrate
- Concentrate
- 250 g
- grams of solid
- Water
- 5 L
- carrier volume
- Batch cost
- £2.50
- 5 L working solution
- Saved vs retail
- £82.50
- 97% · retail £85.00
Estimated coverage at the listed rate: 20 m².
Side-by-Side Price & Potency Comparison
Head-to-head comparison
| Measure | Retail brandedHG | Raw active dupeDupeStack |
|---|---|---|
| Product | HG Rust Stain RemoverAmazon UK search — listing, not a confirmed seller | Oxalic acid dihydrate |
| Pack / unit | 500 millilitres · £8.50 | 1 kg · £9.99 |
| Active | Oxalic acid at 10%Carrier: Water | 99% bulkC2H2O4·2H2O |
| CAS number | Not disclosed on pack | 6153-56-6 |
| Working strength | Ready-to-use pack | Dilute 50 g/L |
| Cost per litre | £17.00 / L typical pack | £0.50 / L mixed from bulk |
| Headline saving | Baseline | 86% cheaper |
| COSHH / PPE | Follow the branded SDS | Gloves. Chemical-resistant gloves (nitrile or neoprene)Eye protection. Indirect-vent splash goggles — not ordinary spectaclesVentilation. Use outdoors or with mechanical extraction |
Active ingredient and cheaper alternative — FAQ
What is the active ingredient in HG?
HG Rust Stain Remover is labelled as Oxalic acid at 10%. The carrier is Water. Pack size: 500 millilitres. The bulk equivalent we index is Oxalic acid dihydrate (CAS 6153-56-6).
Is Oxalic acid dihydrate safe on paving?
Used at the listed working strength (50 g/L), the dupe is the same chemistry as the branded pack for paving, porcelain and masonry. That is not a blanket all-clear: read the supplier SDS, wear the listed PPE, keep acids away from hypochlorite, and follow UK HSE/COSHH rules. Wellness teardowns are supplements, not medicines.
Is there a cheaper alternative to HG Rust Stain Remover?
Yes. The bulk equivalent is Oxalic acid dihydrate (CAS 6153-56-6). Indicative saving 86% per working litre versus a typical £8.50 pack. Working strength: 50 g/L. Live shop prices move.
How do you mix the HG Rust Stain Remover dupe stack?
Toxic if swallowed; wear gloves and goggles. Keep away from children and pets. Dissolve 50 g of crystals per litre of warm water (about 5% w/v) for a patio rust wash. Apply, dwell 10–20 minutes, agitate, then rinse thoroughly with plenty of water. Do not mix with bleach (toxic gases) or use on marble that you care about — it etches carbonates. Store dry. Neutralise spills with bicarbonate, then rinse.
DupeStack provides chemical concentration data and educational mixing guides. Always review official manufacturer Safety Data Sheets (SDS) and comply with UK Health and Safety Executive (HSE) and COSHH regulations when handling concentrated substances. Some links on this site are affiliate links.
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DIY stack · 86% / L vs branded
£24.97indicative kit · Amazon cannot add a mixed search kit as one basket