Pressure washing removes dirt with force, while soft washing removes it with chemistry at low pressure. Hard, durable surfaces such as plain concrete are good candidates for pressure. Roofs, painted stucco, siding, screens and delicate stone usually do better with a soft wash, because the problem there is living growth that a cleaning solution kills, not caked-on grime that needs to be blasted off.
How the two methods differ
Pressure washing uses a concentrated stream, often from 2,000 to 4,000 pounds per square inch (PSI) on gas-powered equipment, to knock dirt, algae and old coatings off a surface. Water volume and a fine tip give it cleaning power, and the operator controls distance and angle. It works quickly on tough surfaces.
Soft washing uses a pump that delivers a high volume of water at pressure not much higher than a garden hose, mixed with a detergent and usually sodium hypochlorite (the active ingredient in household bleach) plus a surfactant that helps the mixture cling. The solution is left to sit, kills algae, mildew and bacteria at the root, and is then rinsed. Because the growth is destroyed rather than scraped off, results tend to last longer on surfaces where algae is the issue.
Which surface gets which method
| Surface | Better method | Why |
|---|---|---|
| Plain concrete driveway or sidewalk | Pressure, with a surface cleaner | Durable; stains need force plus pre-treatment |
| Concrete pavers | Moderate pressure, surface cleaner | Strong enough for dirt, but joint sand is easy to blast away |
| Painted stucco | Soft wash | High pressure can lift paint and drive water into hairline cracks |
| Asphalt shingle roof | Soft wash only | Pressure strips granules; ARMA advises against it |
| Tile roof | Soft wash | Pressure can crack or shift tiles and push water under them |
| Vinyl or aluminum siding | Soft wash or low pressure | Avoid spraying upward under laps |
| Wood fence or deck | Low pressure, or soft wash | Soft fibers splinter and furrow |
| Screen enclosure | Soft wash and soft brush | Mesh and frames are easily damaged |
| Windows and door seals | Low pressure rinse | Water can bypass weatherstripping |
| Dumpster pads, loading docks | Hot-water pressure | Grease needs heat and force; wastewater must be controlled |
Many jobs use both: a soft wash on the house walls and roof and a pressure surface cleaner on the driveway and walkways. A single visit combining methods is one reason to hire a professional who owns both sets of equipment.
Why this matters in a humid climate
South Florida's weather is hard on exteriors. According to the National Weather Service in Miami, the rainy season runs from about mid-May to mid-October and brings most of the year's rain, and humidity stays high even in the drier months. Algae and mildew regrow quickly on stucco, roof tile and shaded concrete. High pressure can strip the surface growth, but it often leaves roots behind and roughs up the surface, which provides more places for spores to take hold. A soft wash that treats the growth tends to buy more clean months. For details on what is growing on your walls, see the guide to mold and mildew on exterior surfaces.
The chemistry, plainly
Soft-wash mixes are often based on sodium hypochlorite. It works, but it has to be handled carefully.
- Plants. Bleach burns foliage. Wetting plants first and rinsing them afterward reduces the harm, and covering delicate ones helps.
- Metals and finishes. Bleach can stain or corrode some metals, discolor wood and fade some paints. Rinse thoroughly.
- Mixing. Chlorine bleach should never be mixed with ammonia-based products or acids, which release toxic gases.
- Alternatives. Some providers use oxygen-based or surfactant-only cleaners for sensitive jobs. They can be gentler, though they may not be as effective on heavy algae.
Runoff from either method should be managed. County rules prohibit non-stormwater discharges to drainage systems, and the runoff rules page explains what that means in practice.
Questions to ask a provider
- Which method do you plan to use on each surface, and why?
- What is the maximum pressure you will use on stucco, windows and the roof?
- What cleaning solution are you using, and how will you protect landscaping?
- How will you manage wash water?
- Does your insurance cover damage to the property?
A provider who answers these specifically has usually done the work before. Vague answers such as "we use whatever it takes" are a signal to keep looking. The guide on hiring a company adds more checks.
The do-it-yourself angle
Home soft-wash kits exist, but handling bleach mixtures and rinsing roofs from a ladder is a different level of risk than washing a driveway. If you do work on your own property, the do-it-yourself guide covers equipment and safety basics.
Frequently Asked Questions
Is soft washing really safe for stucco?
It is generally the gentler option, because it relies on low pressure. Rinse thoroughly, watch for hairline cracks where water could enter, and avoid spraying upward into window frames.
What PSI is considered soft washing?
There is no official cutoff. The term usually means pressure comparable to a garden hose, often well under 500 PSI at the surface, with the cleaning done by the solution.
Does soft washing kill algae or just remove the look?
The cleaning solution is designed to kill algae and mildew at the root, which is why results often last longer than a pressure-only rinse. Regrowth is still possible.
Can pressure washing damage paint?
Yes. High pressure can lift or peel paint, particularly if it is old or poorly adhered. Soft washing is usually used before repainting.
Which method costs more?
It varies. Soft washing may cost more per job because of chemicals and care, while pressure surface cleaning is quick on flat surfaces. Ask for a breakdown by surface.