GPM & PSI

[Kevinsaint 2]

Okay this is going to be an odd one. So, I’m relatively new to the pressure washing industry but have a decent entry level knowledge about most things pressure washing related. Until I started researching on the internet about pressure washing i honestly never realized how essential bleach (or SH whatever you prefer to say) is to a large percentage of pressure washing businesses. Here’s the catch, I’m actually allergic to bleach.. My parents found out when I was a kid because I started breaking out in hives and had other allergic reactions when in contact with bleach in anyway. Which is obviously unfortunate because I understand how much more timely efficient using bleach is versus just pressure from a pressure washer. I want to still continue my pressure washing business because i genuinely enjoy the work. I am just am going to have a take a different chemical approach that works for me. My question is, if I am relying more on the power washer rather than chemicals to wash a house should I still more concerned about GPM or PSI? I’ve heard many times GPM is king but isn’t that more for the rinsing and applying chemical aspect of it? Maybe not. But I’ve been stuck on this decision. I am looking at two machines. One is 4GPM 4000 psi, and the other is 5.5GPM 3000 psi. Which would be better for residential use only when using only the power washer and soap? I will be doing siding, decks, fences, driveways, sidewalks, but no roofs. Which do you guys think will get the job done faster in my situation? More PSI or more GPM? Thank you 

[Beth n Rod 1,279]

It is unfortunate that you have that allergy so in terms of what you are asking, there comes another aspect you need to be aware of.
Pressure on siding forces water behind it. That is bad. The siding is a system of J channels that overlap and have no ability to keep water out when it is forced up under each clap board lap of siding. This is why we use chemicals to do the work and prefer soft washing in order to limit the liability created by pushing water behind the siding where it can get to the sheathing which is mostly particle board or plywood. Yes, there is a moisture barrier wrap installed but the one thing I have found is it is not consistent.
Many contractors installing tyvek or whatever name brand house wrap before siding goes on actually skip the upper floors and gables and in some cases the whole house if the inspector is not due to be back before they can make up for lost time due to weather.

Bleach is a part of the solution we use. There is a number of other ingredients involved to help clean. Just like doing dishes and laundry, there are cleaners for specific stains and clothing types. This plays into our field in that we largely only focus on removing mold, mildew and algae which are the common conditions house siding incurs. There is a detergent, a degreaser, a foaming agent and a rinse aid. Each plays a part in the cleaning process and most of all helps to ensure that not only is the siding clean, no bleach is left behind to be reactivated upon any subsequent moisture event.

Now, in answering your question about GPM vs PSI, there is a rule of thumb. GPM helps to rinse and wash faster because you are using more water to do the job. PSI is used to address issues that require pressure to remove. In the instances of what you are planning to do, psi will play little in that role. But! Before you jump to higher gpm, you will have to ask one question: What are the supply capabilities of the residents flow? There are some out there that have flow restrictors which won't feed your machine the gpm it requires. The other option is to have a buffer tank that you can arrive with and fill while applying chems to get ahead of that. Some use trailer configurations (personally I hate them due to neighborhood road/parking conditions which don't allow much room to navigate. Others use a van with a weight capability to support the large load of a tank. A gallon of water weighs 8 pounds so multiply that times the tanks capacity and compare to the cargo capacity and let that guide you.

I have two versions we use since we do commercial in addition to residential which is our primary focus. A sprinter van which has a 200 gal tank and a chevy 2500 which only has a 30gal tank. Each serves a purpose accordingly and both are 3500psi 4gpm+ units by Hydrotek. We also have a simple drag around unit which is a 4000psi, 4gpm unit to supplement when we need additional guns on the task.

The correct soaps and in many cases bleach will be required to address the many conditions you will encounter. To avoid the issues of allergic reactions, not only for yourself but any employees as well: PPE (Personal Protection Equipment). Rain gear, gloves (Determine which you have no allergies to. We use Nitrile) and rubber boots to keep your feet dry.
The other item which will help as well is a face shield. These are costly but less so in the long run considering the medical outlays or time lost.

Let me know if you have any questions.

Rod & Beth

[Kevinsaint 2]

Okay that makes sense. I planned on using a buffer tank regardless for either. maybe 65 or 100 gal I’m not sure yet depending on what I find locally, for the bypass system and to ensure I get proper GPM in case if the customer has low GPM from the spigot. In theory, where the siding overlaps, what if I were to just agitate with a brush and cleaner and use low PSI To rinse? To ensure no water seeps behind the siding? I don’t know if that makes sense i am just trying to make this work as efficiently as possible ya know? I’m sure there are precautionary steps to take to prevent that? Thank you for your time I really appreciate it 

[Beth n Rod 1,279]

The best advice I can give is to look into vinyl siding manufacturers on the subjects of: Installation, maintenance and recommended cleaners for the types of siding installed.
Aside from vinyl, there is aluminum, composites such as Hardiplank and cementatious coatings such as E.I.F.S. (Exterior Insulatative Finish System) or brand names such as Dryvit and common other versions called Stucco.

There is much to learn in regard to washing houses and learning about their construction including familiarization with IRC residential and local codes helps one to become a better cleaner and less of a creator of damage or liability.
We only use low pressure from two options. One is an M-5 Jet which is for application of the cleaners. The other is a rinse tip and at times a shooter tip which is a 0° tip with a larger orifice to help throw water up high.
Pressure never really exceeds 60-100 psi given the range from tip to surface.

Rod & Beth