Pressure Washing Mix

I’m new to pressure washing and to not cause ANY damage I will be conservative with my 1.) pressure and 2.) chemical mix. My question is how do I achieve 1-2% 12.5 chlorine mix through downstreaming. If I mix 3 parts 12.5, 2 parts water and 1 part Simple Cherry…how much is being diluted through downstreaming? Hope this question makes sense. Basically, wondering what is the proper mix to achieve 1-2% 12.5 when downstreaming.

Thanks to the experienced guys out there!

Welcome aboard mate!
To bad you didn’t hear about last night’s Webinar titled, “Adding Roof Cleaning to Your Business”.

I’m sure you’ll get an answer soon.

My usual mix (for 5 gallons) is 2 gallons of 12% sodium hypochlorite, 3 gallons of water, and 16 ounces of Simple Cherry powder. Premix the Simple Cherry into one of the gallons of water to aid dissolving. For really bad mold/mildew I will go up to 3 gal SH/ 2 gal water.

The keys to getting a decent downstreaming ratio depends on a good injector, a high GPM gun, and not too long a hose run.

Hope that helps.

Thanks Thad…are there any others out there that can put their 2 cents in about their preffered mix? Micha?? And I know it depends on what surface you are cleaning…I guess I’d like to start with a standard baseline…

My mix is the same as Thad’s… Only slighty adjusted for an 8gpm rig.

Ive been using that same mix from the start, its hard to beat.

I just got my new PWasher from Bob. I’m getting ready to try my first batch of this stuff. I’m wondering if this mix since it has chlorine in it will hurt any plant life? Also, where is the best place to get liquid chlorine at? I guess you call it sodium hypochlorite?

the Chlorine can and will hurt the plant life if you dont take precautions. make sure you saturate the areas around the house with water…make sure you cover all runoff areas…do this both before you use solution and after you rinse. You can usually get the chlorine at pool supply stores.

Is this Chlorine a must? Do I need to use it every single time I house wash? I’m a little leery of using it if it’s not necessary. Don’t want to pay for any landscaping.


I learned the formula on here also…from the guys above. Its a great formula…been using it 2 years and never had an issue. Its no biggie…just spray everything down with the wand before and after. especiallly with mold and algae…the chlorine takes it off with ease…check out a couple of the videos…I think Micah has and I think tony also

Thanks Dave

If anyone can point me in the direction of a video that shows how to mix this stuff correctly that would be great. I tried to find them in the video section but no dice.

Where can I buy 12% sodium hypochlorite?

Clorox bleach is only 5-10%.

Go to your local pool-supply store.

Make sure its fresh too. If I recall correctly, SH naturally degrades to about 6% after a certain amount of time. That’s why most bleach at the supermarket is rated at about 6%.

Is there a formula to figure out the percentages your putting on the wall, using different size injectors and gpm’s?

I bet if you turn Thad, Ron, or Micah upside-down and shake them, a formula or hundred will fall out.

Haha, I’m sure thats true, and a bunch of other “stuff” on top of that!

Nothing is 100% accurate across the board due too all the variables.

If you want to be exact, you should fill up a 5 gallon bucket with water, and time how long it takes you to empty that bucket with your downstream injector. Then you can compare that time with the GPM of your machine. Once you know exactly what percentage you’re pulling thru the injector, you can calculate your ratio of cleaners to mix into the 5 gallon bucket for cleaning.

Again, nothing’s perfect, because you don’t know what % your “12.5%” really is due to it’s short shelf life.

SO a general rule of thumb would be, you want to see the mold and algae dissapear after about 5 or 7 minutes of dwell time. Any slower and your mix is probably too weak, and faster and it’s too strong.

I’m trying to pull everything Thad and Micah said together into one post, and I did a little math on my own…let me know if I got it right or wrong.

[B]Pressure Washing Cleaning Solution Recipe[/B]

2 gallons of fresh 12.5% sodium hypochlorite
3 gallons of water
16 ounces of Simple Cherry powder

The sodium hypochlorite must be new or “fresh” because its strength breaks down quickly in storage.

Pre-mix the Simple Cherry in one of the gallons of water to aid dissolving. Add the sodium hypochlorite and remaining water. For really bad mold/mildew, increase the strength of the cleaning solution by using three gallons of sodium hypochlorite and two gallons of water.

[B]Determining the Amount of Cleaning Solution Applied[/B]

If you want know the exact amount of solution you are applying, fill up a 5-gallon bucket with water, and time how long it takes you to empty that bucket with your downstream injector. Then, compare that elapsed time with the gallons-per-minute (GPM) rating of the pressure washer. Once you know exactly what percentage you’re pulling through the injector, you can calculate your ratio of cleaners to mix into the 5-gallon bucket for proper cleaning.


Let’s say you have a 5 GPM pressure washer, and it takes 15 minutes to empty a 5-gallon bucket of cleaning solution. The total amount of liquid applied to the house is determined as follows:

[U]5 gallons[/U] x 15 minutes = 75 gallons

Since five of those gallons were solution, 70 gallons must have been water. Next, determine the ratio of water to cleaning solution.

[U]70 gallons[/U] = 14 or a 14:1 ratio
5 gallons

[U] 5 gallons[/U] = .06666… or approximately 7%
75 gallons

Thus, the ratio of water to cleaning solution was 14:1. Looking at this another way, approximately 7% of the liquid applied was cleaning solution.

If it takes less than 15 minutes to empty your bucket, then the ratio is higher than 14:1; if it takes longer, then the ratio is less than 14:1. The formula above will help you determine the ratio for your pressure washer/injector/tip combination.

The keys to getting a decent downstreaming ratio are a good injector, a high GPM gun, and a short downstreaming intake hose.

While these calculations are helpful, they will only provide an approximate calculation of your cleaning solution strength because you don’t actually know the real strength of your “12.5%” sodium hypochlorite due to its relatively short shelf-life.

As a general rule of thumb, you want the mold and algae to disappear after about 5-7 minutes of dwell time. Any slower than this indicates that your mix is probably too weak (add more sodium hypochlorite); any faster means it’s too strong (add more water to your downstreaming bucket).

This was awesome, I’ve been looking for a thread just like this. Thank you

[MENTION=803]Thad[/MENTION] So if you are using 12.5 SH and cutting it 60/40 with water isn’t that like using 5% bleach, slightly weaker than store bought. I’m kinda confused because I always thought the mix was 3 gal SH and 2 gal water.