How to Power Wash Metal Cladding: Pressure Settings to Avoid Damage

You look at your industrial unit. It is covered in green algae, traffic film, and grime. You rent a heavy-duty diesel pressure washer. You aim the lance at the wall and squeeze the trigger. The dirt vanishes instantly. But ten minutes later, you notice something else has vanished: The top layer of paint.

Metal cladding (especially Plastisol-coated steel) is soft. It is essentially a textured plastic skin glued to a steel sheet. If you hit it with the same pressure you use on a concrete driveway, you will strip the coating, force water into the building's insulation, and create permanent "tiger stripes" on the façade.

Cleaning cladding is not about Force; it is about Flow. Here is how to wash a building without destroying it.

1. The Number One Enemy: The Turbo Nozzle

Before you start, check the end of your lance. Does it have a rotating nozzle (a Dirt Blaster / Turbo Tip)? Throw it away.

A Turbo nozzle spins a zero-degree pencil jet at high speed. It hits the surface with the force of a laser cutter.

• On Concrete: It cuts through moss.

• On Cladding: It cuts circles into the soft Plastisol coating. It can even slice through the rubber seals on windows and skylights.

• The Rule: Always use a Fan Tip (usually 25° or 40°). This spreads the impact over a wider area, acting like a broom rather than a chisel.

2. Pressure Settings: Turn It Down

Most industrial pressure washers run at 3000+ PSI (Bar). This is too high for cladding. You are looking for Low Pressure, High Volume.

• The Ideal Pressure: Aim for 1000 – 1500 PSI (roughly 70–100 Bar) at the nozzle.

• The Distance: Keep the lance tip at least 12 inches (30cm) away from the surface.

• The Logic: You want enough pressure to rinse the chemical away, but not enough to mechanically abrade the surface. If you see the paint colour changing or the water turning the colour of your roof, STOP immediately.

3. The Hazard: Forcing Water Up the Laps

Your roof and walls are made of overlapping sheets. They are designed to shed water running down. They are not designed to stop water firing up. If you blast the wall from the ground aiming upwards, or aim the lance incorrectly on a roof:

1. You drive high-pressure water under the overlap (the lap joint).

2. The water bypasses the butyl seal.

3. It soaks the insulation inside the wall (Rockwool/PIR).

4. Result: You have a clean building on the outside, but a sodden, rotting mess on the inside.

The Technique: Always spray at a 45-degree angle or downwards where possible. Never blast directly into a vertical lap joint.

4. Let the Chemical Do the Work

You shouldn't be using water pressure to remove the dirt. You should use water pressure to rinse the dirt. The heavy lifting must be done by a chemical Traffic Film Remover (TFR).

1. Apply TFR: Use a low-pressure sprayer to coat the wall in a dedicated Cladding Cleaner.

2. Agitate: Use a soft-bristled extending car brush. This physically loosens the static bond of the dirt without scratching the paint.

3. Dwell: Let it sit for 5 minutes (don't let it dry).

4. Rinse: Now use your pressure washer. Because the chemical has broken the bond, the dirt will flow off easily with low pressure.

5. Avoiding "Tiger Stripes"

We have all seen buildings that look stripey after cleaning. This happens when you rely on pressure instead of chemicals. You clean one strip perfectly, but miss the bit next to it.

• To Avoid Stripes: Clean the wall in systematic sections (e.g., one bay width at a time).

• Rinse Top to Bottom: Gravity is your friend.

• Chemical Bottom to Top: When applying the cleaner, work from the bottom up to prevent streaks running down the dry dirty wall (which can stain).

Conclusion

A clean building adds value. A stripped building costs a fortune to repair. Treat your cladding like the paintwork on a car, not the pavement outside a pub. If you have to stand close and blast it to get it clean, you are using the wrong chemical.

• Ban the Turbo Nozzle

• Lower the PSI

• Use a quality TFR