Guides

Pressure Washing vs Soft Washing: Which One Your Surface Needs

The actual difference

Pressure washing is force. Water at somewhere between 1500 and 4000 psi physically knocks material off a surface. It is fast, it is satisfying, and on the right surface it is exactly right.

Soft washing is chemistry. A cleaning solution is applied at low pressure, typically under 500 psi, left to dwell so it can work, then rinsed off gently. The solution does the removal. The water is only there to carry it on and rinse it away.

They are not competing versions of the same service. They solve different problems.

When pressure washing is correct

Hard, non porous, structurally sound surfaces where the soiling is physical rather than biological:

Concrete driveways and paths. Stone flags. Block paving, at controlled pressure. Asphalt. Concrete car park decks. Loading bays. Industrial plant and machinery. Wheel arches and chassis.

On concrete, a rotary surface cleaner rather than a bare wand is what separates a good job from a striped one. The wand leaves visible bands unless the operator is unusually careful. The surface cleaner spins two jets under a shroud and cleans evenly.

When soft washing is correct

Anything fragile, and anything where the problem is alive:

Roofs, always. No exceptions. See below.
House siding, render and stucco. Pressure drives water behind panels and into window seals.
Old brick and stone. Soft mortar does not survive pressure.
Timber decking and fencing. Pressure raises the grain and leaves permanent furring.
Painted surfaces. Pressure strips coatings, often in patches, which looks worse than the dirt.
Decorative tiling. Common on European facades and terraces, and easily destroyed.

Roofs are the one that costs people real money

Those black streaks on an asphalt shingle roof are not dirt. They are algae, usually Gloeocapsa magma. You cannot rinse them off, because the organism is living in the shingle.

Pressure washing them does two things. It temporarily removes the visible staining, and it removes the protective mineral granules that are the entire reason the shingle lasts twenty years. You have traded a cosmetic problem for a structural one, and you have almost certainly voided the manufacturer's warranty in the process.

The streaks then return, often within a year, because the organism was never killed. Soft washing kills it. If a company offers to pressure wash your roof, decline, and treat it as information about the rest of their work.

How to tell which one you are being sold

Ask directly: "what pressure will you use on this, and are you applying a cleaning solution?" A contractor who soft washes will answer immediately and specifically, because it is a deliberate method they have equipment for.

Watch for the word "just" as in "we'll just give it a blast". That is a single method being applied to every surface, which is how damage happens.

What we do

Both, chosen by surface. Driveways, paving and hard standing get pressure and a rotary surface cleaner. Roofs, siding, render, old masonry and timber get soft washed. It is the same hourly rate either way, so there is no incentive to pick the faster method over the correct one, which is a large part of why we price by the hour.