Soft Wash
Soft washing is a low-pressure exterior cleaning method that uses biodegradable detergents and a controlled bleach solution to kill the algae, mold, mildew, and bacteria that cause staining — rather than scouring them off with brute force. A soft wash rig delivers cleaning fluid at roughly 60-200 PSI, comparable to a strong garden hose, which is safe on siding, shingles, painted surfaces, screens, and caulking. The chemistry does the work: the solution dwells on the surface, breaks down the organic growth at the cell level, and is then rinsed clean with fresh water.
In depth
For roofs, Portland cedar, stucco, and older painted homes, soft washing is the only method endorsed by most manufacturers and manufacturer associations. High-pressure washing on these surfaces voids warranties, blasts off granules, forces water behind siding, and shortens the life of the substrate by years. A proper soft wash looks gentle but delivers dramatically better long-term results.
How this shows up on our jobs
Soft wash is the default method we use for every house wash, roof cleaning, and painted-surface job we book in the Madison area. It is the backbone of our residential exterior cleaning process.
Services where this matters
Related terms
Downstreaming
Downstreaming is the technique of injecting soap or cleaning solution into the pressure washer's water line on the low-pressure side of the pump — downstream from the pump, hence the name. A chemical injector pulls detergent from a bucket through a siphon hose whenever a low-pressure (soap) nozzle is attached. When the technician swaps to a high-pressure nozzle, the injector automatically stops drawing chemical, allowing for a clean rinse without switching lines.
Sodium Hypochlorite
Sodium hypochlorite (NaOCl) is the active ingredient in household bleach and the primary disinfectant used in professional soft washing. It is sold to exterior cleaners in 12.5% concentration (commonly called "SH" or "pool shock"), roughly twice the strength of consumer bleach. When applied in a properly mixed soft-wash solution, it kills algae, mold, mildew, lichen, and bacteria at the cellular level within minutes and breaks down into salt water and oxygen.
Surfactant
A surfactant (short for "surface-active agent") is a chemical compound that lowers the surface tension of water so it can wet, spread, penetrate, and cling to a dirty surface instead of beading up and running off. In exterior cleaning, surfactants are blended with sodium hypochlorite and water to let the mix "stick" to vertical surfaces long enough for the bleach to kill organic growth at depth.
Dwell Time
Dwell time is the interval between applying a cleaning chemistry to a surface and rinsing it off. It is the single most misunderstood variable in exterior cleaning. Chemistry does not clean instantly; it needs time to break chemical bonds, kill organisms, or dissolve minerals. Too little dwell and the chemistry is wasted. Too much dwell — especially in direct sun — and the chemistry can damage the surface, bleach landscaping, or drive the stain deeper.
Pressure vs. Volume
Pressure (PSI) and volume (GPM) are the two fundamental outputs of a pressure washer, and understanding the tradeoff between them is the single biggest step an amateur can take toward professional-level results. Pressure is the force of water hitting a single point; volume is the amount of water moving across a surface over time. A high-PSI, low-GPM machine cleans a tiny spot aggressively — great for lifting paint, terrible for washing a driveway. A moderate-PSI, high-GPM machine cleans broadly and gently — great for siding, wood, and most large surfaces.