Most pressure washing jobs use sodium hypochlorite (bleach), surfactants, degreasers, and occasionally oxalic acid. The chemical depends entirely on the surface and the type of stain, not the PSI of your machine.
Pressure washing isn’t just blasting water at high pressure. In many cases, the cleaning power comes from the chemical solution. The pressure simply rinses everything away. When people rely only on PSI, that’s when siding gets damaged, and wood gets scarred.
Sodium Hypochlorite: The Standard for Mold and Algae
The most common chemical used in pressure washing is sodium hypochlorite. It’s the industry standard for removing mold, mildew, and algae from siding, roofs, fences, and concrete.
If you see green buildup on vinyl siding or black streaks on shingles, this is typically what professionals use. But it’s never applied straight. It’s diluted properly and often combined with a surfactant so it sticks to the surface instead of running off.
Contractors usually apply it using a downstream injector or soft wash system to control the mix ratio. That control is what separates professional results from damage.
Surfactants: Why Soap Matters More Than You Think
Surfactants are soap agents added to pressure washing chemicals to improve performance. They help the solution cling to the surface, increase dwell time, and break down dirt more effectively.
Without a surfactant, bleach runs down siding too quickly and loses effectiveness. With one, coverage improves, and chemical waste decreases.
For contractors, this means more consistent results. For homeowners, it means safer and more even cleaning.
Degreasers For Oil, Gas, and Heavy Stains
When it comes to oil stains on driveways or grease buildup on commercial surfaces, bleach won’t help much. That’s where degreasers come in.
These are typically alkaline cleaners designed to break down petroleum-based stains before rinsing. Professionals often apply degreaser first, allow it to dwell, and then rinse with appropriate pressure.
If you’re dealing with garage floors or restaurant pads, this is the chemical category that actually works.
Oxalic Acid: Removing Rust and Brightening Wood
Rust stains from irrigation systems or fertilizer require a different approach. Oxalic acid is commonly used to remove rust from concrete and brighten wood after cleaning.
It’s effective but must be handled carefully. Acid-based cleaners should never be mixed with bleach. Proper sequencing and rinsing are critical.
This is one of the areas where understanding pressure washing chemicals prevents costly mistakes.
Chemicals vs Pressure: What Actually Does the Cleaning?
Chemicals do the cleaning. Pressure rinses it off.
If you try to remove algae using only high PSI, you’ll damage siding before the stain disappears. That’s why soft washing has become standard for roofs and delicate surfaces. Lower pressure combined with the right chemical produces better results with less risk.
Is It Safe to Use Pressure Washing Chemicals?
Yes, when used correctly.
Proper dilution, protective gear, and controlled application make these chemicals safe and highly effective. Landscaping should be pre-rinsed, mix ratios should be accurate, and incompatible chemicals should never be combined.
The danger usually comes from guessing, not from the chemicals themselves.
Can You Pressure Wash Without Chemicals?
You can, but your results will be limited.
Water alone removes loose dirt. It won’t fully eliminate mold spores, and oil stains won’t disappear. That’s why pressure washing chemicals are used in the first place — they target specific types of contamination that water alone cannot handle.
Choosing the Right Approach For Contractors and Homeowners
If you’re a contractor, chemical control is just as important as machine power. Consistent application through proper injectors and nozzles improves cleaning speed and results.
If you’re a homeowner, understanding what chemicals are used in pressure washing helps you decide whether a job is DIY-friendly or better left to a professional.
The surface determines the solution. Not the pressure rating on your machine.
Start with the right chemical. Then apply the right pressure.
