Why a Pressure Washer Alone Isn't Enough
Oil is hydrophobic — it doesn't mix with water. Running a pressure washer over an oil stain spreads it and rinses the surface water, but leaves the oil essentially intact. Effective oil stain removal requires a degreaser to chemically break the oil/concrete bond before the water wash removes the loosened contaminant.
Materials You'll Need
- Industrial concrete degreaser or alkaline cleaner (sodium metasilicate-based products work well)
- Wire brush or stiff deck brush
- Pressure washer with 15–25° nozzle (or turbo nozzle for old stains)
- Protective gloves and eye protection
Step-by-Step Stain Removal
- Absorb fresh spills first: Apply cat litter, sawdust or sand to any fresh spill and leave for 2–4 hours. Sweep and dispose. This removes the bulk of the oil before it penetrates.
- Apply degreaser: Spray or pour concentrated or diluted degreaser (follow label) over the stained area. Ensure full coverage extending 10 cm beyond the visible stain boundary (oil penetrates further than the surface stain indicates).
- Agitate: Work the degreaser into the concrete with a stiff brush. For old, set stains: let the degreaser dwell for 15–30 minutes before brushing.
- Pressure wash: Start at the edges of the treated area and work inward to contain the emulsified oil. Use a 15–25° nozzle at 20–30 cm distance. Multiple passes are usually needed. The water will appear dark and oily — this is the contamination being removed.
- Repeat if needed: Old, set stains may need 2–3 treatment cycles. Each cycle removes a percentage of the residual — complete removal of a years-old oil stain may not be possible without grinding or acid etching.
Environmental Responsibility
Oily rinse water must not be allowed to enter storm drains or surface water drains. Collect using drain plugs and a wet vacuum, or allow to soak into soil/gravel away from drains. Disposing of oil-contaminated water into stormwater drains is illegal in most EU jurisdictions.
FAQ
Does hot water pressure washing remove oil better?
Yes — significantly. Hot water (60–80°C) combined with a detergent emulsifies oil much more effectively than cold water. If oil stain removal is a regular requirement (workshop floor, loading bay), a hot water pressure washer is worth the investment.