The Complete Guide to Jet Washing Your Home's Exterior

Aug 24
5 min read

Jet washing is one of the most satisfying jobs in home maintenance. It is also one of the easiest to get wrong, because the same machine that makes a driveway look new can strip render, force water behind pointing and leave permanent marks on soft stone.

The skill is not in the washing. It is in knowing which surfaces want pressure, which want chemistry, and which want to be left well alone.

This guide runs through the whole exterior of a typical home, surface by surface.

Pressure washing versus soft washing

Everything below depends on this distinction, so it is worth getting clear first.

Pressure washing uses water at high pressure to physically remove dirt. It suits hard, robust, non porous surfaces where force is not going to cause damage.

Soft washing uses low pressure, often little more than a garden hose, combined with cleaning solutions that kill algae, moss, lichen and mould at the root. The surface is treated rather than blasted, and the growth dies off and weathers away over the following days and weeks.

Soft washing is slower to show results and far better for delicate surfaces. It also lasts longer, because it deals with the biology rather than just the appearance.

A good rule of thumb: if the surface is porous, painted, coated, jointed with soft mortar, or made of something you could scratch with a coin, think soft washing.

Driveways, paths and patios

The classic pressure washing job, and generally the safest.

Concrete, concrete block paving and clay pavers all take pressure well. Natural stone varies enormously, with Indian sandstone and limestone much softer than people expect. Porcelain is tough. Tarmac is easily damaged by close range high pressure. Pattern imprinted concrete is sealed, and the seal is the thing at risk.

Use a fan nozzle rather than a pencil jet, keep a consistent distance, and use a rotary surface cleaner attachment for an even finish. Pre-treat moss and algae rather than relying on force. And remember to replace kiln dried sand in block paving joints once the surface has dried.

Brickwork and stone walls

Approach with caution, and be honest about the age of the property.

Modern brick with hard cement mortar can usually take moderate pressure. Older brickwork, particularly anything built with lime mortar, cannot. Lime mortar is deliberately softer than the brick, and high pressure will wash it straight out of the joints. Repointing a wall costs vastly more than cleaning it.

Water forced into masonry also has to go somewhere, and in older solid wall construction that often means inside. Damp problems caused by over enthusiastic washing are a genuine and common outcome.

For most brick and stone, a soft wash approach with a biocide treatment is the sensible choice.

Render, pebbledash and painted masonry

Do not pressure wash these. It is the single most common expensive mistake.

Modern silicone and acrylic renders have a thin coloured finish. High pressure removes it, leaving patches that cannot be tidied up without recoating the whole elevation. Pebbledash loses its aggregate. Painted masonry loses its paint.

These surfaces are exactly what soft washing exists for. A biocide treatment kills the green growth, the surface lightens over the following weeks, and nothing is stripped or forced behind the finish.

Roofs

Roofs are best treated by professionals, and not mainly because of the cleaning.

Working at height is the highest risk part of any exterior cleaning job, and it needs proper access equipment and training. Beyond that, pressure washing roof tiles removes the protective surface of concrete tiles, dislodges bedding on ridge tiles and forces water under the laps into the roof space.

Where roof cleaning is appropriate, soft washing with a moss treatment is the standard approach, along with clearing loose moss from gutters afterwards.

Gutters, fascias and soffits

uPVC fascias and soffits clean up beautifully, but not with a lance held close. High pressure at height forces water behind the boards and into the roof space, and can crack older brittle plastic.

Use low pressure, a soft brush on an extension pole, and a suitable cleaner. Green staining on uPVC responds better to a cleaning solution than to force.

Gutters need clearing rather than washing. Remove debris, check the outlets, and flush through. Blocked gutters cause more damage to a house than dirty walls ever will.

Windows and frames

Never point a high pressure lance at window seals. Water gets past the gaskets, and double glazing units that mist up internally cannot be cleaned. They have to be replaced.

Windows are a low pressure job, and pure water fed pole systems do the work far better anyway.

Decking and timber

Timber is soft and fibrous. High pressure lifts the grain and leaves a fuzzy, splintered surface that then holds dirt worse than before.

Use a wide fan, low pressure, and work along the grain rather than across it. Better still, use a dedicated deck cleaner, a stiff brush and rinsing. Allow the wood to dry fully before applying any oil or stain.

Fences and garden walls

Timber fencing has the same issues as decking, with the added risk of blowing panels apart at the joints. Composite fencing is more tolerant. Rendered garden walls follow the render rules above.

Conservatories

Glass and frames need gentle handling, and the seals around a conservatory roof are exactly the kind of joint that high pressure defeats. Low pressure and appropriate cleaning solutions only.

Practical points before you start

Water restrictions. During a hosepipe ban or temporary use ban, pressure washing from a mains supply is usually restricted. Check with your water company.

Backflow protection. Connecting a pressure washer to a mains tap has water regulations implications, and machines are normally fed via a suitable break or through an appropriate device to prevent contaminated water flowing back into the supply.

Runoff. Dirty water and cleaning chemicals should not end up in a surface water drain that leads to a watercourse. Direct it appropriately.

Neighbours and cars. Overspray travels a long way. Cover what matters, close windows, and think about where the wind is going.

Plants. Wet down and cover planting near anything you are treating chemically.

Safety. Eye protection, sturdy footwear, and never on a ladder with a pressure washer in your hands. The recoil is real.

When to bring someone in

Doing the driveway and patio yourself on a Saturday is entirely reasonable. The jobs that are worth handing over are the ones where a mistake is expensive or the work is at height: render, roofs, older brickwork, conservatories, anything above ground floor, and any surface you cannot confidently identify.

Firms working as pressure washing specialists in London will normally assess the material first and switch between pressure washing and soft washing accordingly, which is really what you are paying for. The machine is the cheap part. Knowing when not to use it is the expensive part.