Patio & exterior
Wet & Forget Exterior Surface Cleaner dupe
Why pay around £34.00 for Wet & Forget? The bulk active is Benzalkonium chloride (BAC 50) — 88% less per working litre than a typical shelf pack.
From the retail pack to the active and the mix
1 · Retail
Wet & Forget Exterior Surface Cleaner
5 litres · £34.00 typical snapshot
Water
2 · Active
Benzalkonium chloride
8% on the label
68424-85-1C22H40ClN
Bulk Benzalkonium chloride (BAC 50)
3 · Mix
1:9
£0.40 per working litre · 88% less than the shelf pack
- Active
- Benzalkonium chloride
- CAS
- 68424-85-1
- Dupe
- Benzalkonium chloride (BAC 50)
- Saving
- 88% / 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.
Label teardown
What the pack promises versus what the label chemistry actually is.
The marketing claim
“No scrubbing, no pressure washing — just spray and walk away”
The chemical reality
A dilute quaternary ammonium biocide sold as a lifestyle patio product. The active is commodity BAC 50; the brand is paying for the trigger bottle and the television advert.
Active vs filler
8% Benzalkonium chloride · 92% carrier / filler — Water
- Typical retail
- £34.00
- 5 litres
- Estimated active cost
- £3.20
- Scaled from bulk £19.99 / 5 litres
- Indicative markup
- 10.6×
- Snapshot maths, not a live shop price
The Marketing Claim & The Catch
A 5 litres pack of Wet & Forget Exterior Surface Cleaner typically retails around £34.00 in patio & exterior. That is a UK shelf-price snapshot for the maths on this page — not a live shop quote or a manufacturer RRP. Listings, sizes and deals move. The marketing line is that you are buying a finished lifestyle product, not a weighed chemical.
On the pack: No scrubbing, no pressure washing — just spray and walk away; Kills mould, algae, lichen and mildew on exterior surfaces; and Bleach-free formula that keeps working in the rain.
The catch: A dilute quaternary ammonium biocide sold as a lifestyle patio product. The active is commodity BAC 50; the brand is paying for the trigger bottle and the television advert.
- “No scrubbing, no pressure washing — just spray and walk away”
- “Kills mould, algae, lichen and mildew on exterior surfaces”
- “Bleach-free formula that keeps working in the rain”
Proprietary Blend & Dosage Breakdown
The labelled active is Benzalkonium chloride at 8%. Everything else in the pack is water.
At 8% 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 50% Benzalkonium chloride (BAC 50), mixed to 1:9.
- Labelled active
- Benzalkonium chloride
- 8%
- Carrier
- Water
- Retail pack
- 5 litres · £34.00
The Active Chemical Alternative (Dupe Stack)
The dupe stack is Benzalkonium chloride (BAC 50) at 50% bulk. Indexed as CAS 68424-85-1, formula C22H40ClN. Buy it as 5 litres for around £19.99 from Amazon UK.
Working strength: 1:9. Indicative cost £0.40 per diluted litre — 88% 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.
- Put on nitrile gloves and splash goggles before opening the concentrate.
- Work outdoors or in a well-ventilated area. Do not mix with bleach, acids or anionic detergents.
- Measure 1 part BAC 50 into a clean sprayer, then add 9 parts water (e.g. 500 ml concentrate + 4.5 L water for a 5 L sprayer).
- Invert gently to mix. Apply to a dry patio until surfaces glisten; do not rinse.
- Leave to weather. Algae and lichen typically collapse over 2–7 days. Repeat on north-facing stone if needed.
Dilution recipe
5 L sprayer
Working strength 1:9. Educational estimate from the listed ratio — check the SDS before you mix.
Chemical
500 millilitres
Benzalkonium chloride (BAC 50)
Water
4.5 litres
Carrier / diluent
10% concentrate · 90% water by working volume (solids are dissolved into the water share).
Required PPE
Loading calculator…
Side-by-Side Price & Potency Comparison
Head-to-head comparison
| Measure | Retail brandedWet & Forget | Raw active dupeDupeStack |
|---|---|---|
| Product | Wet & Forget Exterior Surface CleanerAmazon UK search — listing, not a confirmed seller | Benzalkonium chloride (BAC 50) |
| Pack / unit | 5 litres · £34.00 | 5 litres · £19.99 |
| Active | Benzalkonium chloride at 8%Carrier: Water | 50% bulkC22H40ClN |
| CAS number | Not disclosed on pack | 68424-85-1 |
| Working strength | Ready-to-use pack | Dilute 1:9 |
| Cost per litre | £6.80 / L typical pack | £0.40 / L mixed from bulk |
| Headline saving | Baseline | 88% 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
Is Wet & Forget the same as Patio Magic?
Same molecule family: both are benzalkonium chloride (BAC, CAS 68424-85-1) patio biocides. Wet & Forget is labelled around 8% BAC; Patio Magic around 10%. The DIY stack is the same drum of BAC 50 — only the dilution maths differs (1:9 vs 1:4 from 50%).
Will BAC kill black spot lichen on sandstone?
BAC collapses green algae and soft growth. Deep black lichen dots on sandstone are often a hypochlorite job (see Hagesan Black Spot), not a walk-away quat. Do not mix BAC with bleach.
How do you mix the Wet & Forget Exterior Surface Cleaner dupe stack?
Put on nitrile gloves and splash goggles before opening the concentrate. Work outdoors or in a well-ventilated area. Do not mix with bleach, acids or anionic detergents. Measure 1 part BAC 50 into a clean sprayer, then add 9 parts water (e.g. 500 ml concentrate + 4.5 L water for a 5 L sprayer). Invert gently to mix. Apply to a dry patio until surfaces glisten; do not rinse. Leave to weather. Algae and lichen typically collapse over 2–7 days. Repeat on north-facing stone if needed.
DupeStack provides chemical concentration data and educational mixing guides only. Wellness pages compare food supplements, not medicines or prescribed treatments. Always review the supplier Safety Data Sheet (SDS) and comply with UK Health and Safety Executive (HSE) and COSHH regulations when handling concentrated substances. Mixing and storage are at your own risk. Some links are affiliate advertisements (Amazon Associates, eBay Partner Network, and Awin when those programmes are live). Commissions do not change listed concentrations or calculator output.
Related guides
Patio guide
Patio cleaners decoded: BAC, DDAC, bleach, acid and degreasers
Which patio bottle is which molecule? Benzalkonium, DDAC, hypochlorite, brick acid, metasilicate, strippers and a silane sealer — matched to DupeStack teardowns.
Patio guide
How much patio chemical do you need? Measure first
Convert a patio or drive into m², then into concentrate and water using DupeStack teardowns and the area estimator.
Patio guide
BAC vs DDAC vs bleach on patios — which active for which stain?
Quat biocides, twin-chain DDAC and hypochlorite do different jobs on paving. When to use each — and what never to mix.
More teardowns
Patio & exterior
Patio Magic!
Patio Magic
- Retail pack
- £24.995 litres
- Raw active
- Benzalkonium chloride (BAC 50)68424-85-1
Another BAC patio biocide in a different coloured bottle. Same quaternary ammonium as Wet & Forget; same bulk drum of BAC 50. You are paying for the brand, not a different molecule.
Patio & exterior
HG Rust Stain Remover
HG
- Retail pack
- £8.50500 millilitres
- Raw active
- Oxalic acid dihydrate6153-56-6
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.
Patio & exterior
Hagesan Black Spot Remover
HG
- Retail pack
- £24.995 litres
- Raw active
- Sodium hypochlorite 14–15% (industrial / dairy grade)7681-52-9
Standard commercial bleach solution sold at five times agricultural merchant prices.
£44.97Save 88% / L
Indicative DIY stack