Soft Wash vs Jet Wash: What’s the Difference?

The Two-Sentence Summary

Jet washing blasts dirt off the roof surface using water at 1,500–3,000 psi — about 15–30 times the pressure of a garden hose. It looks instantly impressive, but the pressure also strips off the protective glaze on concrete tiles, cracks ridge mortar, and forces water into spots it shouldn’t be.

Soft washing uses biocide chemicals at very low pressure (under 100 psi — less than a garden hose). The chemicals kill the algae, moss and lichen at the root. The dead growth either rinses away gently or weathers off naturally over 2–6 weeks. No surface damage, no force, no compromised seals.

What Jet Washing Does To Your Roof

The reason we never use jet washers, even when the customer asks:

• Strips the protective glaze off concrete interlocking tiles. The glaze is what makes the tile waterproof and slows moss regrowth. Once it’s gone, the tile soaks up water and regrows moss within 12–18 months — faster than before cleaning.
• Cracks mortar on the ridge tiles. You won’t see it from the ground. You will see it as a leak through the bedroom ceiling in winter 2027.
• Forces water under tile laps and flashings. Some of that water doesn’t come back out.
• Breaks ridge tile bedding. Many jet-washed roofs need full ridge re-bedding within 2–3 years — a £800–£1,500 repair job.
• Strips moss spores from the surface but leaves the roots. Regrowth is faster after a jet wash than after no cleaning at all.

Why Some Cleaners Still Use Jet Washers

• It looks impressive instantly — great for before-and-after social media photos
• It’s faster on the day — 2 hours vs 6 hours for soft wash
• Cheap equipment — a domestic jet washer is £200; a professional soft wash setup is £3,000+
• The damage shows up later — usually after the warranty period and outside the “can I get a refund” window

How To Tell If A Cleaner Uses Jet Washing

• Ask directly — an honest cleaner will tell you exactly what method they use
• Watch for “power washing” or “pressure washing” in their adverts — same thing
• Look at their equipment — a soft wash van has plastic chemical tanks and low-pressure pumps; a jet wash van has petrol-driven high-pressure equipment
• Beware low prices — if it’s under £250 for a typical semi-detached, they’re probably jet washing

Is Soft Washing Always The Right Choice?

For roofs — yes, almost always. For driveways and patios, high-pressure washing is fine and standard practice; the surfaces are designed for it. For brickwork and render, soft washing is also the right approach. The key rule: if the surface is sealed or glazed, soft wash it.

Related Reading

• Our roof cleaning service in detail
• How much does roof cleaning cost in Hampshire?
• Frequently asked questions