Concrete looks bombproof, but it is more porous and more temperamental than most Cape Town homeowners realise. Get the pressure and technique right and a grey, algae-stained patio or driveway comes up looking almost new. Get it wrong and you etch permanent tiger stripes into the surface. Here is how to clean concrete properly, and where the quirks catch people out.
Why concrete needs a lighter touch than you think
Concrete drinks in water, oil and dirt because it is full of tiny pores. That is why stains sink in and why algae and mould take hold so easily on the shaded, damp side of a house through our wet winters. It also means too much pressure held in one spot will blast out the cement paste and leave you with a rough, pitted patch that never matches the rest. The goal is to lift the grime sitting in and on the surface without carving into the concrete itself.
For a full driveway, our driveway pressure cleaning approach is the same principle scaled up. If your patio is pavers or slasto rather than a poured slab, the technique shifts a bit; see our pool deck and paver patio cleaning page for that.
Pressure, nozzles and distance
Sound concrete handles a fair amount of pressure, but the nozzle you choose matters more than the machine's top rating. Skip the pencil-thin zero-degree tip on flat concrete; it cuts lines you cannot undo. A 25-degree fan tip is the workhorse, and a surface cleaner attachment, the round wheeled unit that looks a bit like a floor polisher, gives you an even finish with no wand marks across a big slab.
- PSI: around 3000 psi is plenty for most residential concrete. More is not better.
- Nozzle: a 25-degree fan tip for general work, or a surface cleaner for large flat areas.
- Distance: keep the tip roughly 20 to 30 cm off the surface and move steadily; never park it in one place.
- Motion: overlapping sweeps in one direction so you do not leave a stripey, patchy finish.
Always test a hidden corner first. Older or already-flaking concrete can react badly, and it is better to find that out behind a pot plant than in the middle of the driveway.
Oil, rust and that chalky white bloom
Water alone rarely shifts the stains people actually care about. Oil drips under the car and rust marks off a gate hinge or garden furniture need a pre-treatment: a degreaser worked in with a stiff broom and given ten minutes to bite before you rinse. Hot-water machines lift grease far better than cold if you have access to one.
The chalky white haze that appears on concrete and face brick is efflorescence, mineral salts drawn to the surface as the slab dries out, and it is common here after our wet winters. Blasting it harder does not help. A light wash and a dedicated efflorescence or mild acidic cleaner does the job, and it often returns until the concrete has fully cured or dried out for the season.
Seal it once it is properly dry
Sealing is the step most people skip, and it is the one that keeps concrete clean for longer. A sealer fills those open pores so oil, salt off the coastal air and algae have far less to grab onto, which means easier washes down the line. Let the concrete dry completely first, ideally a couple of warm, rain-free days, then apply the sealer. Trapping moisture under a sealer causes a cloudy, blotchy mess, so patience pays.
Do the maths on time, too. A decent concrete clean is a half-day job once you factor in pre-treating stains and letting cleaners work. If you are hiring or buying a machine anyway, weigh that against having it done properly in one go.
Frequently asked questions
What PSI should I use on a concrete driveway?
Around 3000 psi is ample for sound residential concrete. Chasing a higher rating just increases the risk of etching the surface. The nozzle choice and keeping the tip moving matter far more than raw pressure.
Can pressure washing damage concrete?
Yes, if you hold a narrow, high-pressure jet too close or linger in one spot. That blasts out the cement paste and leaves a rough, pale patch that will not match. Use a wider fan tip or a surface cleaner, keep the tip 20 to 30 cm away, and move steadily.
How do I get oil stains off my concrete?
Pre-treat with a degreaser, scrub it in with a stiff broom and let it sit for around ten minutes before rinsing under pressure. Fresh spills lift easily; older, soaked-in stains may need a second round or a hot-water machine, which handles grease much better than cold.
Should I seal concrete after pressure washing?
It is worth it. Sealing closes the pores so oil, coastal salt and algae struggle to take hold, and it makes future cleans easier. Wait until the concrete is fully dry, a couple of warm rain-free days, or you will trap moisture and get a cloudy finish.
Want it done right? See our driveway and concrete cleaning service, get a free quote, or call us on 079 616 7761.