Karcher K5 vs Nilfisk C135 for Cleaning Indian Sandstone Patios

What the pressure number does on sandstone

Indian sandstone sold through UK and Australian merchants such as London Stone and Marshalls is commonly riftsawn or hand-dressed. Calibrated slabs run from 18mm to 30mm thick, and the exposed face keeps a natural grain that takes up water at uneven rates.

That variation shows up between familiar colours. Kandla Grey, Raj Green, and Modak do not all resist washing in the same way, even when they were bought as the same paving type. The denser greys usually tolerate cleaning better than the warmer, softer stones.

The Karcher K5 Premium is rated near 145 bar and moves roughly 500 litres per hour. The Nilfisk C135.1 sits around 135 bar with a comparable flow. On a sound slab laid on a full mortar bed, both machines can clean the surface at a sensible lance distance without cutting into the face.

The damage pattern is easy to recognise. A zero-degree pinpoint jet held within 50mm lifts the softer matrix between harder quartz grains, leaving a pale, frosted patch with a rougher feel. Once that face is eroded, washing will not restore the original finish.

The 10 to 15 percent pressure gap between the K5 and the C135 is small beside the effect of spray pattern and standoff. A 25-degree fan held at 200mm will clean Raj Green without scarring. The same washer fitted with a turbo nozzle and held at 80mm can leave visible swirl marks in Modak within seconds.

Both makers include a rotary lance intended for stubborn dirt. Karcher calls its version the Dirt Blaster, while Nilfisk supplies a Tornado PR rotary lance. Each spins a zero-degree jet through a cone, which is why it strips ground-in algae from concrete and block paving quickly.

On Indian sandstone, that same action is the patio installer’s familiar disaster. The spinning point repeatedly crosses the same patch of soft sedimentary stone, so the user may see the algae vanish and only notice the etched track when the slab dries.

The safer setup is the variable fan lance opened wide, or Karcher’s Vario Power lance dialled toward the low-pressure end. Keep the spray moving with the grain of the slab and avoid dwelling on a stained spot. Use an offcut or a hidden corner first, since Modak and Raj Green erode faster than the denser greys. A dedicated patio cleaner left to dwell for ten minutes loosens biofilm, allowing the rinse to stay gentle.

A fan-lance pressure reading at a fixed 200mm on soft sedimentary stone would be more useful than the headline pressure printed on the carton. Without that value, the offcut or hidden-corner test remains the practical guide to how a particular slab will react.

Jointing usually suffers first

Whichever washer is used, jointing sand and weak mortar pointing are likely to move. Re-sanding or re-pointing with a polymeric jointing compound in the same week keeps water from tracking under the slabs and lifting them during frost.

Flow, motors, hoses, and water supply

Flow rate decides how quickly loosened dirt rinses away. The K5 and the C135 both deliver around 440 to 500 litres per hour at the trigger, so a 30 square metre patio differs by only a few minutes over a full clean.

The Karcher K5 carries a water-cooled induction motor. It runs quieter and tolerates longer continuous sessions than the universal motor found in many entry-level machines. That matters when the patio, paths, garden furniture, and drive are cleaned in one session.

The Nilfisk C135 uses a more conventional motor and a click-and-clean bayonet fitting for nozzles. Lance changes are quick, especially compared with the push-fit arrangement on older K-series units. For a user swapping between a fan lance and detergent application, that fitting is one of the Nilfisk’s more noticeable conveniences.

Hose length has a bigger effect on the job than many buyers expect. The K5 ships with around 8 metres on an integrated reel. The C135 typically comes with 6 metres loose. On a long garden run, the extra 2 metres can keep the washer in one place instead of dragging it across wet, freshly cleaned paving and marking the surface again.

Do not run either pump dry. Both machines draw from the mains through a standard hose connector, and both rely on trigger release to cut the pump under stall protection. Drawing from a water butt is possible with a suction kit and a filter, with lift height limited to roughly half a metre.

Rinse water from sandstone carries detergent, algae, and fine grit toward the patio edge. Where it runs into adjacent beds, it can compact heavy clay and pool against the slab line. That is part of the clean-up pattern, even in a comparison between two pressure washers, because the water has to go somewhere.

Which washer makes more sense

For a one-off annual clean on a modest patio, the Nilfisk C135 is the simpler buy. Its lower price and lighter weight fit occasional use, as long as the turbo lance stays in the box when Indian sandstone is being cleaned.

For frequent use, longer sessions, and a tidier hose arrangement, the Karcher K5 has the advantage. The water-cooled induction motor, quieter running, and integrated 8 metre reel are the reasons its higher cost can make sense for a larger property or repeated cleaning through the year.

The least helpful number on either specification sheet is the headline pressure. The machines are close enough that technique overwhelms the difference: fan width, distance from the face, detergent dwell time, and keeping the spray moving do more to protect the stone than choosing 145 bar over 135 bar.

A freshly washed patio also exposes every tired edge around it. Old pointing, an algae-streaked wall, and a compacted bed beside the paving become more obvious once the sandstone returns to its quarried colour. The awkward part is that the tool comparison can be neat while the slab response stays uneven across the same patio surface.