SH Chemical Mixing Percentages

Hey guys, I am trying to start my first pressure washing business, and am starting off with a Dewalt DXPW3625. 3600 PSI, 2.5 GPM which I know is very low, however I will be buying a new one once I get the money. What I have been trying to figure out is (Not in the owners manual, also called Dewalt and they did not have an answer for me) if SH is safe for the pressure washer, but not only that I also need to figure out how much the pressure washer dilutes the chemical mixture. So say if I have a 10% SH mixture, and am using my chemical hose/injector that came with the pressure washer to connect it, how much does the pressure washer itself dilute that mixture and what is actually being sprayed onto the concrete?

Usually the manual that came with it can answer the dilution question.

Don’t run bleach through the pump itself, usually the injector is on the outlet of the pump on smaller homeowner units but double check.

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Can’t really add much. But will say dewalt specifically says do not use bleach. Page 12 of owners manual. (If I had right manual) Though can’t really say much without looking at how that one is designed.

Yes it appears to be on the outlet of the pump. However I already went through the entire manual and could not find the answer or even anything regarding chemicals.


My DeWalt is the 3.5gpm /4K psi unit and I started off by running bleach through the pump as I deemed it was only entering the tail-end of the pump as the pressurized water was exiting the pump.

I ended up getting the hi-draw injector kit from PressureTek and installed it right off the pump. I happen to have found that for me, I can leave the old barb on the pump and not have to mess with it and my draw rate with the new injector is just fine. Some people on here have advised that it may be necessary to cover or block off the old barb so keep that in the back of your mind.

Edit: I believe my manual stated the pump injector would create a 20:1 mix, but don’t hold me to that - and of course, yours could absolutely be different. The bucket test with a low pressure nozzle would be the way to determine yours draw rate for sure.

Dustin is right, only clean water runs through the pump. The dilution is going to vary depending on your unit’s downstream injector. It’s also only going to pull the mixture at low pressures, I think around 100 psi and below. You’ll need to do a bucket test with your soap tip to see what it actually draws.

Edit: I was wrong about 100psi. Google says the cutoff is closer to 800psi on some injectors

More than that, my injector still draws at 1200psi. Thankfully I have a remote valve.

May I ask what a bucket test is and how to perform it?

Honestly, it’s not as important to know the percentage of a given mix as it is to know what works. Most people will probably agree that a 1.5% (ish) mix is good for vinyl. And around a 3% mix is food for pre-treating or post-treating concrete. However if your bleach is old, if you’re getting 10% vs 12.5%, how much hose you’re running, the specific chem injector, etc all affect the results specific to your setup. My suggestion would be to fill a few different buckets with different ratios of bleach and water and test out what the minimum affective dose is. So maybe one bucket is pure SH, one is 50/50, and the other is 30/70. Test each one on vinyl or concrete or whatever and see what works. Also, the injector goes after the pump, usually at the reel. That way SH is only being drawn into the hose and not the pump. Just my two cents! Best of luck to you.

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Fill up a quart jug of water, put your DS injector in it. Use a soap tip and spray into a 5-gallon bucket (or two) until the quart is empty. Then measure how much total water you sprayed (minus a quart), and that gives you your ratio. For instance, if you end up with 13 quarts total in the bucket, that would be 12:1

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What I described above is different than a “bucket test” for gpm, obviously

When’s the last time you replaced it? May be time for a new one. That’s the problem though, they CAN still draw at higher pressures that would not be safe to use on most residential siding. That’s why doing it the lazy way and not using a valve, remote switch or just walking back to the trailer and putting the draw tube in a bucket of water can be so risky. If I remember correctly you need around a 300psi pressure differential to stop the soap. If yours draws at 1200 then you’d need roughly 1500 to stop drawing soap. 1500psi is not soft washing in my opinion. But some on here believe that it’s all groovy and won’t cause any problems and they use tips to up their pressure and stop the flow.

Who me? I need it on there.

Your injector. Is it an older one or relatively new?

I’ve gone through several the past couple years, why?

Who left the door unlocked?


They wear out just like everything else. I flush mine after every job and still have to replace often.

Ahh okay. Thank you for the help

No problem. When you figure out your ratio, you can divide your SH mix strength by the total number of parts. Meaning, if you’re getting 12:1 and spraying 10% SH undiluted, you’d divide 10 by 13. So you’d get 10 / 13 = .76% SH and that’s a great place to start for vinyl

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