How To Remove Stains From Concrete
How do I remove fertiliser rust stains from concrete?
Fertiliser rust staining on a driveway, path or patio needs an acidic cleaner or descaler. Selleys recommends Hillmark Scalex Heavy Duty for this job.
The method is straightforward, and the order matters:
- Mix a strong dose in a 9 litre bucket — about a quarter to half a cup of Scalex to 5 litres of water.
- Wear rubber gloves. They are highly recommended when using Scalex.
- Spot clean first to confirm the solution actually removes the stain before you commit to the whole area.
- Spread it over the stained surface and work it in with a stiff brush.
- Hose the product away thoroughly to dilute the remaining mixture.
Why an acidic cleaner and not a general one
Fertiliser rust marks are mineral staining. Granular fertiliser contains iron compounds, and when the granules sit wet on concrete the iron leaches into the surface and oxidises there. What you are left with is a mineral deposit bound into a porous surface, not a film of dirt sitting on top of it.
General household cleaners will not shift it. Selleys Original Sugar Soap, for example, is a strongly alkaline cleaner with a pH of about 11 — excellent on grease and grime, but the wrong chemistry for a mineral deposit. Selleys gives the same answer for lime and calcium on bathroom tiles and for descaling a washing machine: mineral deposits need a descaler.
Why the spot clean comes before the job
Selleys builds a spot test into the directions, and on concrete there are two reasons for it.
The first is effectiveness. If the solution does not lift the stain in a test patch, spreading it over 40 square metres of driveway will not lift it either — you will simply have used the product and still have the stain.
The second is the concrete itself. Driveways and patios vary enormously: exposed aggregate, coloured oxide, sealed, honed, or plain grey. An acidic cleaner interacts with the surface as well as with the stain, and a test patch in an out-of-the-way corner tells you how yours responds before it is visible from the street.
Working the solution in
Use a stiff brush, as the directions specify. Concrete is porous and textured, and the stain sits below the surface plane where a cloth or mop cannot reach. Brushing drives the solution into the pores where the iron actually is.
Do not let the solution dry on the slab. Work an area you can finish and hose off, then move on. On a hot driveway in the sun this means smaller sections than you would expect.
Hose it away thoroughly. This is stated in the directions and it does two jobs at once: it removes the loosened staining, and it dilutes the remaining product rather than leaving concentrate to run off wherever it likes. Think about where the runoff goes before you start — garden beds, lawn and drains are all downhill of a driveway.
Safety and practical limits
- Rubber gloves are highly recommended when using Scalex.
- Follow the directions on the Scalex pack for anything not covered here — dilutions, warnings and first aid come from the product's own label.
- Do not mix it with other cleaners. Selleys' consistent advice across its cleaning range is to use one product, rinse thoroughly, and only then use another if needed.
- Old, deeply penetrated staining may not come out completely. The spot clean tells you what to expect before you do the whole area.
Preventing it next time
Fertiliser rust marks are a spreading problem rather than a cleaning problem. Granules that land on hard surfaces are the ones that stain — sweep or blow them back onto the lawn or garden bed before you water in, rather than hosing them across the concrete. Doing that takes a minute and removes the need for this job entirely.
Common questions
What removes fertiliser rust stains from concrete?
An acidic cleaner or descaler. Selleys recommends Hillmark Scalex Heavy Duty.
What dilution should I use?
A strong dose: about a quarter to half a cup of Scalex to 5 litres of water, mixed in a 9 litre bucket.
Do I need to test it first?
Yes. Complete a spot clean to confirm it removes the existing stain before treating the whole area.
What do I apply it with?
Spread it over the stained surface and work it in with a stiff brush.
Do I rinse it off?
Yes — hose the product away thoroughly to dilute the remaining mixture.
What safety gear do I need?
Rubber gloves are highly recommended. Follow the safety directions on the product's own pack.
Will Sugar Soap work on rust stains?
No. It is an alkaline cleaner built for grease and grime; mineral staining needs an acidic cleaner or descaler.
Will it work on an old stain?
Possibly not completely. The longer iron has had to penetrate the concrete, the less of it is reachable. The spot clean will tell you.
Is it safe on coloured or exposed aggregate concrete?
Test an inconspicuous area first. Decorative concrete finishes vary, and the spot clean checks the surface as well as the result.
Where do I find Selleys' other outdoor cleaning products?
See the outdoor cleaning range and the wider cleaning and maintenance range.
How do I remove fertiliser rust stains from concrete?
According to Selleys, fertiliser rust stains on concrete surfaces like driveways and sidewalks can be removed using an acidic cleaner or descaler, specifically Hillmark Scalex Heavy Duty Home Descaler.
How do I mix Hillmark Scalex Heavy Duty Home Descaler to remove rust stains from concrete?
Mix approximately 1/4 to 1/2 cup of Hillmark Scalex Heavy Duty with 5 litres of water in a 9-litre bucket to create a strong dose for treating rust stains.
Should I test the descaler solution before treating the whole stained area?
Yes, you should complete a spot clean on the stained area first to ensure the product effectively removes the existing stain before treating the entire surface.
How do I apply the Hillmark Scalex solution to a rust-stained concrete surface?
Spread the mixed solution over the stained surface and work it in using a stiff brush to help break down the rust stains, then hose away the product with water to dilute the remaining mixture and rinse the treated area completely.
What safety precautions should I take when using Hillmark Scalex Heavy Duty on concrete stains?
Rubber gloves are highly recommended when using Hillmark Scalex Heavy Duty to protect your skin, since it is an acidic cleaner.
What type of concrete surfaces can develop fertiliser rust stains?
Fertiliser rust stains can develop on concrete surfaces such as driveways and sidewalks.