Jet-Washing Your Patio Can Do More Damage Than the Moss You're Trying to Remove

A pressure washer feels like the obvious tool, and it is the one most likely to cause the damage you are trying to avoid. A setting that is fine for porcelain can mark softer stone, and too much pressure on block paving strips out the jointing sand, turning a cleaning job into a repointing job.

Can you pressure wash a patio during a hosepipe ban?

Not in an area under a temporary use ban, and it costs nothing to check first. Thames Water's rules for a ban, for example, prohibit using a hosepipe, sprinkler or pressure washer to clean patios, driveways, paths, walls, windows or other outdoor surfaces. They do not stop you using a bucket and brush, which handles most patios well on its own. Check your own water company's page to see whether a ban is in force, and what it covers, before you start.

What is your patio made of?

Identify the surface before you reach for anything, because the wrong method is usually the cause of the problem you are trying to fix. Manufacturers' guidance differs by material:

The sources are Marshalls for sandstone and block paving, and Mandarin Stone for porcelain and natural stone. If you do not know what you have, test the gentlest method in a corner first.

How do you clean a patio step by step?

1. 1Sweep it. Marshalls recommends regular brushing with a stiff outdoor brush so dirt does not become ingrained.
2. 2Scrub with warm soapy water. Work one section at a time so the water does not run into the borders, scrub firmly and rinse with clean water.
3. 3Let it dry before judging the result. Marshalls says some stones change colour when wet, and drying can take under an hour in summer or overnight in cooler weather.
4. 4Pressure wash only as a last resort, if it is still dirty. Marshalls suggests holding the nozzle 30 to 50cm from the surface and moving slowly across each slab.
5. 5Refill the joints on block paving. Marshalls says washing can displace jointing sand, and recommends brushing in kiln-dried sand.

The RHS adds three cautions worth taking seriously: pressure washing uses a lot of water and energy for a result that does not last, because growth returns if the damp and shade that caused it are still there; the extra water can make damp worse where drainage is poor; and you should wear eye protection.

Should you use bleach or a patio cleaner?

Often not, and the sources do not agree. Marshalls suggests a half-and-half bleach and water mix for heavier moss and algae on Indian sandstone, rinsed off thoroughly. Elsewhere it says to use bleach sparingly and keep it off plants and soil. Mandarin Stone says vinegar and bleach can strip sealants and damage porcelain and natural stone over time. The RHS says chemical patio cleaners are not needed because non-chemical methods work, and notes that most are short-lived, so repeat applications are needed.

A sensible order is to scrub first, test any product in a hidden corner and follow your paving maker's instructions. Marshalls advises keeping cleaner away from plants, grass and wildlife, and it says acid-based products can cause rusting on some sandstone and lighten certain limestones.

Why does the green come back?

Algae and moss follow damp and shade, not dirt, so scrubbing alone only ever buys a few weeks. The RHS says they do not damage the surface but make it slippery, and that letting in light and air is what actually slows regrowth. To slow it:

• Prune overhanging plants so sun and wind can dry the surface.
• Keep drains clear of leaves.
• Brush regularly, which the RHS says stops growth establishing.
• Check the slope. Surfaces that shed water stay cleaner, which is why the RHS suggests a slight fall and channels of coarse gravel along edges.

Weeds in the joints are a separate problem, covered in how to stop weeds growing between paving.

When is it worth getting someone in?

Consider it for a large area, a fragile stone or a surface you cannot reach safely. Too much pressure can mark a surface or break up the sand in the joints, and that damage costs far more to put right than the clean itself. Our jet wash and gutter clearing service starts with a free, no-obligation visit and a written quote.

Sources

• RHS: Algae and moss on hard surfaces
• Marshalls: How to clean your patio slabs
• Marshalls: Indian sandstone, busting the myths
• Marshalls: How to clean block paving driveways
• Marshalls: Garden paving technical information
• Mandarin Stone: Patio care guide
• Thames Water: Temporary hosepipe ban

This article sets out Aspen Rose's own reading of the manufacturer and RHS guidance above, useful background on cleaning paving safely, not professional advice for your particular stone or patio. Every surface is different, so if in doubt, get a free, no-obligation quote and we'll take a proper look.