How do I remove oil and rust stains from a patio?

Matching the treatment to the stain — oil, rust, tannin, paint and efflorescence all behave differently — and what genuinely cannot be removed.

Difficulty: beginner
Time: 1 hr 30 min
Read: 3 min
Safety: caution

Short answer

Draw oil out with an absorbent poultice rather than trying to wash it off. Treat rust with an oxalic-acid based rust remover made for stone. Leave efflorescence alone and it weathers off. Never use acid on limestone or polished stone.

Paving is porous, so most stains are not on the surface but in it. Washing pushes them deeper. The treatments that work either draw the stain back out, or chemically convert it into something soluble.

Safety

Acid-based cleaners burn skin and eyes and damage some stone permanently — wear goggles and chemical-resistant gloves, add acid to water rather than the reverse, and never mix cleaning products. Never allow oil, solvent or acid run-off to enter a drain, pond or watercourse. Test every product on an inconspicuous area first.

Step by step

Identify the stain before treating it.Dark and spreading with a halo: oil. Orange-brown, often under metal furniture or from a fixing: rust. Brown and following the drip line of a tree or a wooden bench: tannin. White powder: efflorescence, not a stain at all.
Test everything on an inconspicuous area.Sandstone, limestone and some concrete products react badly to acid. Try any product on a spare slab or a hidden corner and wait 24 hours before committing to the whole area.
Treat fresh oil by absorbing it.Cover with cat litter, sawdust or a proprietary absorbent granule and leave it several hours before sweeping up. Do not hose it — water spreads the oil and drives it in.
Draw out old oil with a poultice.A thick paste of an absorbent powder and a solvent or degreaser, spread over the stain, covered with plastic and taped down, and left to dry for a day or two. As it dries it pulls the oil out of the stone. Repeat as needed.
Use an oxalic-based remover on rust.Rust removers for stone are usually oxalic acid based. Apply to the wet surface, leave for the stated time, and rinse thoroughly. Do not use on limestone or polished stone.
Deal with tannin with an alkaline cleaner.Wood tannin stains respond to an alkaline patio cleaner or a dilute bleach solution rather than acid. Rinse thoroughly and keep it off planting.
Leave efflorescence alone.The white bloom is salts brought to the surface as the paving dries out. It weathers off over a season or two. Acid washing it can drive the salts back in and make it worse.
Rinse and contain the run-off.Rinse thoroughly with clean water, and use a bund of sand or absorbent socks to keep contaminated run-off out of drains and borders.
Consider sealing afterwards.A breathable impregnating sealer makes future stains far easier to remove. Apply only to clean, thoroughly dry paving, and only after any acid treatment has been fully neutralised and rinsed.

Tips

The poultice method is slow and it is the only thing that reliably works on old oil. Two or three applications is normal.
Metal garden furniture leaves rust marks at every foot. Plastic feet or coasters prevent an annual job.
Photograph a stain before treating it. It is surprisingly hard to judge progress otherwise.

Common mistakes

Pressure washing an oil stain — The water drives the oil deeper into the porous slab and spreads it over a wider area. Absorb or poultice instead.
Using an acid cleaner on limestone or polished stone — Acid dissolves the calcium carbonate in the stone itself, etching the surface permanently. Identify the stone before choosing a product.

If it doesn't work

Stain faded but still visible after cleaning

Cause: Stain has penetrated deeply — Fix: Repeat the poultice two or three times. Deeply penetrated oil in porous stone may never come out completely.

Cleaned patch now lighter than the rest

Cause: The cleaner removed general weathering as well as the stain — Fix: Clean the whole area to even it out. This is why test patches go in inconspicuous places.

White bloom appearing after cleaning

Cause: Efflorescence drawn out by wetting — Fix: Leave it to weather. Brushing off the dry powder helps; acid does not.

Rust returning in the same spot

Cause: A ferrous fixing or inclusion in the slab itself — Fix: Find and remove the metal source. Some stone contains iron inclusions that will rust indefinitely.

Questions people ask

Will bleach clean a patio?

Dilute bleach kills algae and lightens organic stains, and is fine on concrete. It does nothing for oil or rust, damages planting it runs onto, and should never enter a watercourse.

Can old oil stains be removed completely?

Often not entirely from porous stone. Repeated poulticing lightens them substantially. A sealer applied afterwards prevents the next one going in as deep.