Why ‘a bottle should be enough’ fails
Retail packs quote optimistic coverage. Your north-facing sandstone is not a brochure patio. Weigh or measure the surface, then run the maths against the same active you intend to buy in bulk.
Three steps
1. Measure length and width in metres (or use a preset: 5×4 patio, 6×3 drive strip). 2. Pick a teardown whose active matches the job (BAC/DDAC for film, not brick acid for algae). 3. Open the area estimator or calculator in area mode — read concentrate, water and batch cost.
Then buy the bulk drum or sack sized for that batch, not twelve trigger bottles.
Safety still wins
Quat biocides are toxic to aquatic life. Keep off ponds, rinse nearby plants when the label says so, and keep pets off until dry. The estimator does not replace the SDS.
FAQ
- Is a 5 × 4 m patio really 20 m²?
- Yes — length × width in metres. Irregular shapes: split into rectangles or use an average width. The estimator has presets for common sizes.
- Why does coverage differ between brands?
- Each teardown carries square metres per working litre (or grams per m²) from the mixing spec. Porous stone and heavy growth drink more — treat calculator output as indicative and check the SDS.
More patio & exterior guides
Patio guide
Patio cleaners decoded: BAC, DDAC, bleach, acid and degreasers
Patio guide
BAC vs DDAC vs bleach on patios — which active for which stain?
Patio guide
When to use a metasilicate degreaser on driveways
Patio guide
Driveway oil stains: degreaser vs solvent vs absorbent
Patio guide
Water-repellent, biocide or acid — which patio job needs which chemistry
Patio guide
Driveway & TFR oil and grease: which solvent for which stain
Related teardowns
Live stacks this guide points at — mix maths and DIY affiliate links on each page.
Patio & exterior
Wet & Forget Exterior Surface Cleaner
Wet & Forget
- Retail pack
- £34.005 litres
- Raw active
- Benzalkonium chloride (BAC 50)68424-85-1
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.
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
4-in-1 Patio Power
Jeyes
- Retail pack
- £16.004 litres
- Raw active
- Didecyldimethylammonium chloride (DDAC 50)7173-51-5
This is not old Jeyes Fluid (tar acids are gone). Patio Power is 1.75% DDAC — a twin-chain quat, not the benzalkonium in Patio Magic. Dilute DDAC 50 to about 0.35% and you have the same working spray as the 4 L bottle mixed 1+4.
Patio & exterior
Organic Path, Patio & Deck Cleaner Concentrate
Algon
- Retail pack
- £11.992.5 litres
- Raw active
- Spirit vinegar 25% (acetic acid)64-19-7
The ‘organic patio cleaner’ is about 18% acetic acid with a drop of sugar-derived surfactant. Dilute 1:3 and you have ~4.5% vinegar. Spirit vinegar at 25% is the same molecule in a 5 litre jerry.
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.
Patio & exterior
Patio, Driveway & Masonry Cleaner
KilrockPRO
- Retail pack
- £14.005 litres
- Raw active
- Sodium metasilicate pentahydrate10213-79-3
This is not Patio Magic (BAC) and it is not Mortar Clen (HCl). KilrockPRO is a dilute alkaline masonry degreaser — disodium metasilicate (CAS 6834-92-0) with soda ash and a chelator. Metasilicate pentahydrate crystals mixed at about 30 g/L match the bottle strength; then dilute 1:20 for light stains as the pack does.
Patio & exterior
Eco Patio & Decking Cleaner
Logco
- Retail pack
- £29.995 kg tub
- Raw active
- Sodium percarbonate (technical oxygen bleach)15630-89-4
Logco’s Eco patio powder is sodium percarbonate (CAS 15630-89-4) — the same solid peroxide adduct as Vanish Oxi, sold as a 5 kg outdoor tub. Fifty grams per litre of warm water is the deck/patio band (about 5 m²/L). It is not BAC, not DDAC and not hypochlorite. A technical 5 kg sack is the same oxidiser without the decking label.
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.