Before the water
A driveway is the most forgiving surface on the house and the easiest to make look amateur. Almost every bad result comes from starting the machine before the preparation is done.
- Sweep it. Loose grit under a surface cleaner becomes shot blasting.
- Wet the beds either side. Runoff carries whatever you put down; dilution is the defence.
- Check where the water goes. Down the drive to a storm drain is the default and, on any commercial site, the wrong answer.
- Test in the corner. Thirty seconds by the garage tells you whether the slab is sound.
Concrete under a year old
Pre-treat first, always
Oil, tyre polymer and engine drips do not come off with water at any pressure — they come off with an alkaline degreaser and time. Apply it to the dry stain, let it work for the dwell the product asks for, and only then bring the machine.
Organic staining is the opposite chemistry: the green and black growth in the shaded half of most drives is algae, and dilute hypochlorite kills it. Some operators pre-treat the whole slab with a weak mix, let it sit while they set up, and find the disc does half as much work.
The pass
A 20-inch surface cleaner on 4 GPM at 3,000–3,500 PSI through a 25-degree green tip set is the standard rig for residential concrete. Walk it at a pace that actually cleans — roughly a foot a second — and overlap every pass by about a quarter of the disc.
| Mistake | How it shows | Fix |
|---|---|---|
| Walking too fast | Faint parallel bands as it dries | Slow down; a second pass costs more than going slowly once |
| No overlap | Sharp untouched strips between passes | Quarter-disc overlap, every pass |
| Disc too big for the flow | Even but thin cleaning; bar audibly slow | Smaller disc, or more GPM |
| Changing direction mid-slab | Visible seam where the two patterns meet | One direction for the whole area |
Edges, joints and the apron
A surface cleaner cannot reach the last inch against a wall, the expansion joints, or the flare where the drive meets the street. Those get done by hand with the wand and a 25-degree tip, after the main pass, working in the same direction so the finish matches.
The apron is where the worst of the staining lives — road film, brake dust, the oil from every car that has ever parked half on. It is also the piece most often left out of the measurement and cleaned anyway. Measure it and charge for it.
Surface damage risk
PSI & nozzle quick reference
- 0 degRed
- Spot jet. Etches most surfaces.4000 PSI
- 15 degYellow
- Stripping bare concrete.4000 PSI
- 25 degGreen
- General concrete and walkways.3500 PSI
- 40 degWhite
- Siding, wood, vehicles.1500 PSI
- ~65 degBlack
- Detergent draw, low pressure.500 PSI
The post-treat that keeps it clean
A cleaned driveway that was green from algae will be green again within a season unless the growth is killed rather than removed. A dilute hypochlorite application after the final rinse — roughly 0.75% at the surface — does that, takes five minutes, and is the difference between a customer who calls back next year and one who calls back next month to complain.
Rinse the landscaping once more afterwards, walk the slab with the customer while it is still wet and dark, and take the after photos from the same positions as the before set. Then send the invoice before you leave.
Where the runoff goes