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.
In depth
There are four broad families — anionic, cationic, non-ionic, and amphoteric — and exterior cleaners almost exclusively use non-ionic surfactants because they tolerate the high pH and chlorine content of a soft-wash mix without breaking down. A good surfactant package gives the solution a visible foam cling (sometimes called "snow foam") that shows the technician exactly where coverage has and hasn't reached, extends dwell time on hot days, and dramatically improves rinse-ability.
How this shows up on our jobs
Every house wash mix we use includes a professional-grade non-ionic surfactant so the cleaner actually stays on your siding and roof long enough to work — not just runs straight to the ground.
Services where this matters
Related terms
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.
Non-Ionic Surfactant
A non-ionic surfactant is a surfactant whose molecule carries no net electrical charge, making it uniquely tolerant of the extreme pH and high chlorine content found in a soft-wash mix. Ionic surfactants (anionic, cationic) often precipitate, react, or lose effectiveness when combined with 12.5% sodium hypochlorite; non-ionics stay stable, keep their foaming action, and continue to reduce the surface tension of the cleaning solution throughout the dwell period.
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.
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.