Pressure Washer Detergent Explained

I've spent 12 years spraying everything from daily drivers to 40-foot hulls, and I've learned that the soap you use matters almost as much as the machine pushing it. Almost.

Pressure washer detergent is the difference between a clean driveway and a stained one, and most people are using the wrong stuff or no stuff at all.

Here's the deal. Detergent isn't just soapy water. It's a chemical that breaks the surface tension of grime so the water can actually lift it off. Skip it and you're just moving dirt around with high pressure. Use the wrong kind and you'll etch your concrete or strip the wax off your car. Use the right kind and jobs take half the time.

How I Tested

I ran five different detergents through three washers over the last two months. My Simpson Megashot with the Honda GC190 for the heavy stuff, my old electric Sun Joe for the siphon tube test, and a borrowed Ryobi 2300 because I wanted to see if the detergent system on a mid-range gas unit made a difference.

I washed the same stretch of concrete driveway, the same section of vinyl siding, and the same boat hull with each one. I timed every job. I took photos before and after. I cursed when the siphon tube stopped drawing.

Simple Green Pro HD

The workhorse. I've used this for years in the detailing business and it's the one I grab when I need to cut through road grime or grease stains on concrete.

Simple Green Pro HD is a heavy-duty industrial formula. It's got a higher pH than the regular green stuff you find in the garage, which means it actually dissolves oil and grease instead of just pushing it around. I sprayed it on a driveway stain that had been there since before I bought my house and watched it lift in about three minutes.

The catch is you have to rinse it thoroughly. If you leave it on concrete in the sun, it dries into a film that's actually harder to remove than the original stain. I learned that the hard way on a customer's patio. Took me an extra hour with a surface cleaner to fix my own mistake.

Buyers report the same thing. One guy on the pressure washing forums wrote in June: "Works great on the driveway but I didn't rinse fast enough and now I've got white streaks." That's user error, but it's worth knowing before you start.

It also works on the boat hull, which is where I really put it to the test. Algae and scum came off in one pass with the 15-degree nozzle. I didn't even need the surface cleaner.

At $28 a gallon, it's not the cheapest option. But you dilute it, so a gallon lasts a while. I use about a quarter cup per gallon of water in the soap tank.

Chemical Guys Mr. Pink

This is the car guy's detergent. It's pH neutral, which means it won't strip wax or etch clear coat. It foams up thick and slick, and it smells like bubblegum, which sounds gimmicky until you're washing a car in the sun and you're not gagging on industrial chemicals.

I use this for customer cars when I'm doing a wash-and-wax package. It's gentle enough for regular use and it doesn't leave spots if you rinse quickly. The foam clings to vertical surfaces, which is the whole point. It gives the soap time to break down the dirt before you rinse.

The downside is it's not strong enough for anything beyond light dirt. I tried it on the driveway and it just sat there. No lifting power on oil stains, no real bite on mold. It's a car soap, not a pressure washer detergent, and you should treat it that way.

Buyers seem to agree. The Amazon reviews are full of people saying "great for cars, useless for concrete." That's exactly right. Use it for what it's for and you'll love it.

One thing to note: it doesn't play nice with every siphon tube. The thicker formula can clog the pickup on cheaper units. I had to thin it out with water in the Sun Joe or it just wouldn't draw. On the Simpson, no problem, but that's a $440 machine with a proper detergent system.

At $20 a gallon, it's reasonable for what it does. Just don't expect it to clean your driveway.

Sun Joe SPX-FC34

This is the detergent that comes with the Sun Joe SPX3000, and it's the default for anyone who bought that $120 electric unit. It's fine. That's the most generous thing I can say.

The SPX-FC34 is a concentrated formula that works with the siphon tube on the Sun Joe's detergent tank. It produces decent foam, it lifts light dirt, and it rinses clean. For washing a car or a small patio, it does the job.

But it's thin. It doesn't cling to vertical surfaces like the Mr. Pink, and it doesn't cut grease like the Simple Green. It's the vanilla ice cream of pressure washer detergents. It's fine, but you're not going to write home about it.

The bigger issue is the siphon tube on the Sun Joe itself. It stops drawing soap after about ten minutes of use. I've had four separate buyers tell me the same thing. The detergent system on the SPX3000 is the weakest part of an otherwise decent budget washer.

If you're using the Sun Joe, I'd actually skip the branded detergent and grab a bottle of the Simple Green instead. It's cheaper per ounce and it works better. Run it through the siphon tube while it's still drawing, then switch to the rinse nozzle when it gives up.

At $12 a quart, the SPX-FC34 isn't a ripoff, but it's not a value either. You're paying for the name on the bottle.

Household Bleach

This isn't a pressure washer detergent, but I'm including it because it's the best thing I've found for killing mold and mildew on siding, and nobody talks about it.

Mix one part bleach to four parts water, add a squirt of dish soap to help it cling, and spray it on the shady side of your house where the green stuff grows. Let it sit for ten minutes, then rinse with the widest nozzle you've got. It'll look like new.

The catch is bleach will kill your plants, stain your clothes, and eat the seals in your pump if you run it through the machine. I only use it with a garden sprayer, never through the pressure washer itself. The bleach will degrade the o-rings in the detergent system and you'll be replacing seals by fall.

I've seen guys on the forums argue about this. Some say a little bleach through the siphon tube is fine. I'm not one of them. I've rebuilt too many pumps to risk it.

If you're dealing with mold on siding, this is the answer. Just don't be an idiot about it. Wear gloves, protect your plants, and rinse everything thoroughly.

The GPM vs PSI of Detergent

Here's where the detergent conversation gets technical. The reason a $450 Simpson with a Honda engine cleans better than a $120 electric isn't just the pressure. It's the volume.

Detergent needs water to carry it. A unit that pushes 2.4 GPM moves more soapy water across the surface than a unit pushing 1.2 GPM. That means more chemical contact, more dwell time, and a better clean.

The Sun Joe SPX3000 pushes 1.76 GPM. The Simpson Megashot pushes 2.4 GPM. That difference is huge when you're trying to keep a vertical surface wet with soap for the full dwell time.

If you're using detergent with a low-GPM unit, you have to work in smaller sections. Spray, wait, rinse, move on. With a high-GPM unit, you can cover more ground and the soap stays wet longer.

This is why I tell people to stop obsessing over PSI and start looking at GPM. The detergent does the chemical work. The water volume does the physical work. PSI is just penetration.

Should You Buy Detergent?

If you're only washing your car once a month, get the Chemical Guys Mr. Pink. It's gentle, it smells good, and it's the right tool for the job.

If you're cleaning a driveway, patio, or siding, get the Simple Green Pro HD. It's the only one in this list that actually cuts through the grime that's been sitting on your concrete since last summer.

If you're dealing with mold, skip the branded detergents entirely and mix up the bleach solution. Just don't run it through the washer.

If you're using a Sun Joe, save your money on the branded detergent and buy something better. The siphon tube is going to give up anyway, so you might as well have a detergent that actually works while it's drawing.

What I'm Testing Next

I'm looking at a few foam cannons to see if any of them actually produce foam that lasts longer than ten seconds. Every video on the internet lies about this. I'm also testing the Chemical Guys Citrus Wash and Gloss, which a few detailers swear by for heavy road grime. If it holds up on the boat hull, I'll add it to the list.

The detergent landscape changes faster than the washers themselves. Check back in a few months and I'll have updated this with whatever I've found.