Pressure Washing Glossary
Industry terms, equipment, and techniques explained clearly
Last Updated: April 5, 2026
This glossary covers the terms you'll hear on the job site. No fluff, no unnecessary jargon — just clear definitions of equipment, techniques, and concepts that actually matter.
Use the search or filter by category to find what you need. Related terms are linked together so you can see how concepts connect. Master these terms and you'll have solid foundation knowledge for the work.
Downstream Injector
EquipmentA chemical injection system that introduces cleaning solution into the water stream AFTER the pump. Lowers pressure significantly (typically 10:1 ratio), making it safer for applying chemicals. Requires a large-orifice nozzle (usually black, 65°) to create sufficient venturi effect for chemical draw.
Upstream Injector
EquipmentChemical injection BEFORE the pump, introducing chemicals into the water stream at high pressure. Not common in residential applications — can damage pump seals and is dangerous. Most contractors use downstream injectors instead.
Venturi Effect
PhysicsThe principle that allows downstream injectors to work: as water velocity increases through a restriction (the injector), pressure decreases, creating a vacuum that pulls chemicals into the stream. Requires proper nozzle sizing and water flow.
Sodium Hypochlorite (SH)
ChemicalsThe active ingredient in bleach and most pressure washing chemicals. Concentrated liquid typically available at 10-12.5% strength from pool supply stores. Diluted to 0.5-3% for house washing depending on application. Primary cleaner for organic growth (algae, mold, mildew).
Surfactant
ChemicalsSurface-acting agent that reduces water surface tension, helps cleaning solutions cling to vertical surfaces, and improves overall cleaning effectiveness. Essential for roof cleaning to prevent runoff and improve dwell time. Often called 'roof soap' or 'foaming soap'.
Dwell Time
TechniqueThe time cleaning solution remains on a surface before rinsing. Critical for effective cleaning — chemicals need time to break down contaminants. Typical dwell times: 5-10 minutes for house wash, 15-20 minutes for roof cleaning. Never let chemicals dry on the surface.
Soft Wash
TechniqueCleaning method using high-volume, low-pressure water (typically 500-1000 PSI) combined with specialized chemicals to clean surfaces. Relies on chemical action rather than mechanical force. Standard for house washing, roof cleaning, and delicate surfaces. Contrasts with 'power washing' or high-pressure cleaning.
Power Washing
TechniqueHigh-pressure cleaning using heated water (if machine has heater) and maximum pressure. Often used incorrectly to describe all pressure washing. True power washing uses hot water which improves cleaning, especially for oil/grease. Not suitable for most residential surfaces.
GPM (Gallons Per Minute)
MeasurementWater flow rate measurement. Critical for cleaning speed — higher GPM = faster cleaning. More important than PSI for most residential work. Typical machines: 2.5-4 GPM. Commercial equipment: 5-8+ GPM. GPM determines how quickly you can rinse and flush contaminants.
PSI (Pounds Per Square Inch)
MeasurementPressure measurement indicating water force. Higher PSI isn't always better — excessive PSI damages surfaces. Most residential cleaning works best at 1500-3000 PSI. Concrete can handle 3000-4000+ PSI. Nozzle selection dramatically affects effective PSI at surface.
Cleaning Units (CU)
MeasurementTheoretical cleaning power calculated as PSI × GPM. Higher CU = more cleaning capability. Example: 3000 PSI × 4 GPM = 12,000 CU. Useful for comparing machines, but doesn't tell the whole story — technique, chemicals, and nozzle selection matter more.
Unloader Valve
EquipmentSafety valve that bypasses water back to the pump inlet when the trigger gun is released, preventing pressure buildup. Can be adjustable (allows pressure changes) or fixed. Critical for pump longevity and safety. Also called 'pressure regulator' or 'bypass valve'.
Surface Cleaner
EquipmentAttachment with spinning bars enclosed in a housing that cleans flat surfaces evenly. Eliminates streak lines from wand cleaning. Sizes range from 12' to 36'+. Standard for driveways, sidewalks, and patios. Must be kept moving to prevent surface damage.
J-Rod
EquipmentTelescoping wand extension for roof cleaning, allowing chemical application from the ground or ladder. Named for its J-shaped tip that directs spray downward. Reduces fall risk and improves chemical application angle. Typically extends 12-24 feet.
X-Jet
EquipmentExternal nozzle/venturi injector system that applies chemicals without going through the pump. Allows strong chemical application (bypasses pump, protects seals) and can reach second story from ground. Popular for house washing before soft wash systems became common.
Post-Treat
TechniqueApplying chemical to specific stains after initial cleaning, typically for stubborn oil, rust, or tannin stains. Allows targeted stronger treatment without exposing entire surface to harsh chemicals. Common on concrete for oil spots and rust stains.
Flash
TechniqueWhen chemical dries on surface before it can be rinsed. Leaves white residue and can damage surfaces. Caused by hot temperatures, direct sunlight, or excessive dwell time. Prevent by working in smaller sections, wetting surrounding area, and timing application appropriately.
Burn
DamageSurface damage from excessive pressure or improper technique. Can include: wood 'furring' (raised grain), etched concrete, stripped paint, blown window seals, scarred siding. Often irreversible. Prevented by proper nozzle selection, distance, and technique.
Etching
DamagePermanent surface marking, usually on concrete, from too much pressure or holding nozzle too close. Shows as darker/lighter pathways where water spray contacted surface. Can be intentional (for decorative purposes) or accidental damage. Difficult to repair.
Furring
DamageWood grain raised and roughed from excessive pressure or improper technique. Makes surface rough, prone to catching dirt, and difficult to refinish. Common on decks and fences with too much pressure. Requires sanding to repair. Prevent with proper PSI and white nozzle.
Overspray
IssueChemical spray carried by wind to unintended areas. Can damage landscaping, vehicles, and neighboring property. Major liability issue. Prevented by: checking wind direction, spraying away from sensitive areas, pre-wetting landscaping, using proper nozzle selection.
Runoff
IssueChemical solution that drains from cleaned surface. Can kill landscaping, enter waterways (environmental concern), and pool in unwanted areas. Must be managed: capture runoff when required by law, divert away from plants, neutralize if necessary.
Neutralize
TechniqueCounteracting chemical (typically SH) after cleaning to protect sensitive surfaces. Common method: rinsing landscaping with fresh water before, during, and after job. Some use chemical neutralizers (sodium thiosulfate) but fresh water dilution is standard practice.
Pre-Wet
TechniqueThoroughly wetting landscaping and surrounding areas before applying chemicals. Saturates plants so they absorb less chemical runoff, and dilutes any chemicals that do contact them. Critical step in house washing and roof cleaning. Combined with post-rinse for maximum protection.
Hot Water Box
EquipmentWater heater attachment that provides hot water cleaning (200°F+). Transforms cold water pressure washer into hot water/power washer. Dramatically improves oil/grease cleaning. Requires propane or diesel fuel. Common in commercial/industrial applications, rare in residential work.
Buffer Tank
EquipmentWater reservoir (typically 50-100 gallons) that ensures consistent water supply to pressure washer. Prevents pump damage from water starvation and allows use where water supply is limited. Common in truck-mounted setups and commercial applications.
Truck Mount
EquipmentComplete pressure washing system mounted in or on a truck/van. Typically includes: large engine, large pump, buffer tank, chemical tanks, hose reels. Allows high flow (5-8+ GPM), higher capacity, faster work. Standard for commercial contractors.
Skid
EquipmentPressure washing unit (engine + pump + frame) designed to be mounted in truck/trailer. 'Skid-mounted' means portable but not handheld. Can be removed from vehicle. Common alternative to full truck mount for contractors who want flexibility.
Browse by Category
Equipment
Machines, attachments, and tools you'll use on the job
Chemicals
Cleaning solutions and their properties
Technique
Methods and best practices for effective cleaning
Measurement
PSI, GPM, cleaning units, and other metrics
Damage & Issues
What can go wrong and how to prevent it