Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
(OP)
Not a on-the-job question, but it relates to concrete wear-and-tear.
Assume a 30-year-old "nominal concrete" driveway, no rebar.
If I am pressure washing it to remove mildew and years of accumulated tree sap and gunk with a "Big Box" rented pressure washer rated at 2000 psi, will the washing force erode the concrete?
Question was asked by she-who-must-obeyed, and a neighbor. My answer was "no."
My reasoning was two fold:
A test area with the nozzle held 1/2 inch from the concrete for 20 seconds showed no erosion of the concrete nor any breaking out of the aggregate from the matrix. Aggregate was already visible at the top of the concrete: it was not "smooth" before testing. Normal nozzle position was 2-3 inches from the concrete being swept side-to-side with a constant but overlapping motion, so in one place for 20 seconds was far in excess of what was normally done. Figure an average total water impact area of 2-1/2 inches x 1/4 inch "fan" when it hit the concrete.
second was my assumption that a 2000 psi washer is putting out 2000 psi at the PD pump outlet. Down a 50 ft, 1/4 internal diameter hose, through hose and washer fittings, and then out the nozzle reduces the pressure even more.
Going out the nozzle itself spreads out the force over a bigger area, and so reduces the final pressure even more. But the water at the nozzle hole is much faster than than the slower water in the hose -> so is the impulse force more important than pressure?
Assume a 30-year-old "nominal concrete" driveway, no rebar.
If I am pressure washing it to remove mildew and years of accumulated tree sap and gunk with a "Big Box" rented pressure washer rated at 2000 psi, will the washing force erode the concrete?
Question was asked by she-who-must-obeyed, and a neighbor. My answer was "no."
My reasoning was two fold:
A test area with the nozzle held 1/2 inch from the concrete for 20 seconds showed no erosion of the concrete nor any breaking out of the aggregate from the matrix. Aggregate was already visible at the top of the concrete: it was not "smooth" before testing. Normal nozzle position was 2-3 inches from the concrete being swept side-to-side with a constant but overlapping motion, so in one place for 20 seconds was far in excess of what was normally done. Figure an average total water impact area of 2-1/2 inches x 1/4 inch "fan" when it hit the concrete.
second was my assumption that a 2000 psi washer is putting out 2000 psi at the PD pump outlet. Down a 50 ft, 1/4 internal diameter hose, through hose and washer fittings, and then out the nozzle reduces the pressure even more.
Going out the nozzle itself spreads out the force over a bigger area, and so reduces the final pressure even more. But the water at the nozzle hole is much faster than than the slower water in the hose -> so is the impulse force more important than pressure?






RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
My guess...the concrete is fine until you hit a spot that might have already started to crack away or break look (near joints, edges, etc). You might lose some concrete here, but not simply erode away the surface.
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
Further, the distance between the nozzle and the surface to be cleaned makes a big difference. The farther away the nozzle is from the surface, the lower the contact impingement pressure will be. Once the distance gets over about 12 to 15 inches, it's affect is similar to a garden water hose with a concentrator nozzle.
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
http://www.cement.org/tech/cct_con_design_powerwas...
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
off-topic. but something my dad brings up everytime we grill at his house. wasn't me.
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
Terry
KI6FCI
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
Terry
KI6FCI
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
@Ron,
At what length hose is the pressure behind the nozzle rated? If the hose is longer, then the pressure is reduced due to the additional head loss in the hose. Also, the head loss at the nozzle is basically the pressure behind the nozzle as once the water leave the tip, it is at atmospheric pressure. All of the pressure has been converted to water velocity (minus heat and sound)
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
Flow rate low, less than 2 gpm so I did not expect much pressure loss due to flow alone, which is why I'd expect - as noted above - that almost all of the potential (pressure) energy is converted in kinetic energy (sound, velocity) at the nozzle exit. Then, as the distance from the nozzle increases and the spray "footprint" increases (see photo of damage from "handwriting" with a pressure washer above) less and less energy is available to impact the concrete.
Many interesting and inciteful comments, my thanks to all who contributed their experiences. Robert
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
As to the pressures involved, the damage that can happen to skin and underlying tissues due to pressure washers (and paint sprayers) is tremendous. Imagine a pint of water or driveway cleaner forced under the skin and into the tissue because you accidentally hit your leg with the tip.
I once saw a guy at a self-serve car wash inflate the brand new paint on the roof of his car like a balloon.
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
A friend of mine likes to tell the story of his friend (professional painter) who was cleaning his airless sprayer of oil based paint. He reached into the bucket of solvent to see if the gun was spraying. After a week in the hospital he was able to keep his arm. The nozzle broke the skin at his wrist and injected paint thinner up his forearm.
Respect your tools and what they are capable of doing.
Terry
KI6FCI
RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?
So, the technical answer is there IS erosion, but for the limited exposure you are applying, the erosion is not discernible.
TTFN

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RE: Pressure Washing 3000 psi Concrete at 2000 psi. Will It Erode?