Surface cleaners: sizing, speed and streaks

A surface cleaner is a shrouded disc with a spinning bar carrying two or four nozzles, running on castors at a fixed height. Because the stand-off never varies, every square inch of concrete gets the same pressure — which is what a hand-held wand can never quite manage — and because it covers a wide swathe at once it works roughly three to four times faster on open flatwork.

The shroud also keeps most of the spray and debris off the siding, the windows and the cars, which saves the second job you would otherwise create.

The bar is driven by the water leaving its jets. Flow, not pressure, decides whether a given disc diameter can be driven properly.

Fitting a disc larger than the flow supports is the single most common equipment mistake in this trade. It feels like an upgrade and produces slower, worse work.

Striping has four causes and only one of them is the machine.

• Walking too fast. The commonest by far. Roughly a foot a second is a working pace.
• No overlap. Overlap a quarter of the disc on every pass, without exception.
• Under-fed disc. The bar audibly slows. Fix the sizing, not the technique.
• Worn or mismatched nozzles. Two jets of different sizes clean two different widths. Replace them as a set.

1. Sweep first. Loose grit under a disc is shot blasting.
2. Pre-treat oil and organic growth and let it dwell while you set up.
3. Pick one direction and hold it for the whole area. A change of direction mid-slab leaves a permanent seam.
4. Keep the disc flat. Tilting it puts one edge closer and cuts a line.
5. Never lift it while running. The bar is spinning and unshielded the moment it leaves the ground.
6. Edge afterwards with a wand and a 25-degree tip, in the same direction as the passes.

A surface cleaner is a flatwork tool and nothing else. It cannot reach the last inch against a wall, cannot follow a curve, cannot do steps, and cannot go up a vertical surface. Every job that uses one still needs a wand for perhaps a fifth of the area, and that fifth takes a disproportionate share of the time.

It is also the wrong tool on anything that is not dense and flat: pavers (it empties the joints), stamped concrete (it hazes the colour coat), asphalt (it lifts the binder), and obviously wood, siding and roofs. Read the surface first; the disc is a choice, not a default.