Pressure washing causing swirls
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  1. #1
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    Pressure washing causing swirls

    I am curious the thinking from the professionals on this:

    I see some brands videos of foam guns spray a car then follow up with high pressure spray down.

    If even a microfiber towel can cause swirl marks , wouldn't high pressure water spray cause marks in the paint?

    Also , if a wipe down with a towel can unless done without utmost care, can cause scratches, with all the technology available constantly , how come paint can't withstand a wipe down with a soft towel without possible scratches.
    I enjoy washing and waxing my cars , but it seems the paint is soo delicate that it can't withstand a wipe down without getting swirl marks unless you baby it ?

    My background is engineering, not that it matters, the more I get into caring for my vehicles, the more I wonder why the paint is so delicate with all the technology I see in many industries .I am not questioning you guys, just wondering. Hard paint, soft paint, they all seem to get swirls and scratches just from one careless dealer wash and prep. Yet, I need to work a bit with a machine to remove that mark.

    Driving down the freeway , I bet tiny sand like particles, and miniscule debris cause fine swirl scratches more commonly than wipe down towels ? Has that been discussed ?

    Just curious , I expect you guys can set me straight.

    Thanks

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    is more old fashioned Tuck91's Avatar
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    Re: Pressure washing causing swirls

    My take on pressure washing is if you can see the lines where you sprayed the paint and where you didnt then your too close to the car.

    I like to stay at least 2ft away from the paint.

    You can get closer when cleaning wheel wells, tires, undercarriage, etc.

    You are spot on in regards to how delicate you must be with most paint.

    A lot of these car wash/tunnel wash type places have brushes that are terrible on the paint and still have dirt sticking to them from the last ten work trucks that went throught it.

    Even most "hand car wash" locations are of poor quality as they dont know or even care about proper appearance care.

    Now imagine taking a nice defect free out of the factory black BMW, and running it through these types of places above once a week for an entire year, makes me cringe just thinking about it.
    Nick
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    Re: Pressure washing causing swirls

    My thought is that when you hand mit, spong or wipe a car down....it seems like everyone uses somewhat of a circular motion. With that being said, I see some the scratching caused that way.

    Going back 20 years ago with my uncle who was a 50s something anal renentive bacholor with a 435hp black laquor Corvette Roadster, he rubbed and rubbed in straight lines with his lint rags and diapers. He got me into that kick back then for a few years and I had straight lines too for whats that worth. Now I'm lazy and lost the touch of having swirl free and scratch free stuff.

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    Re: Pressure washing causing swirls

    Quote Originally Posted by Tuck91 View Post

    Now imagine taking a nice defect free out of the factory black BMW, and running it through these types of places above once a week for an entire year, makes me cringe just thinking about it.
    show me a defect free car straight out of the factory other than a Bentley or a Rolls.

    I agree with keeping pressure washer away from the paint at least a foot or 2. why take the chance of catching a paint chip and peeling off more paint.

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    Cool Re: Pressure washing causing swirls

    hmmm, editing problem
    Last edited by the other pc; Jul 20th, 2011 at 07:42 PM. Reason: won't let me delete

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    Cool Re: Pressure washing causing swirls

    OK, let’s try this again...

    Quote Originally Posted by 2011Murano View Post
    ...If even a microfiber towel can cause swirl marks , wouldn't high pressure water spray cause marks in the paint?...
    A swirl mark is a collection of very fine scratches in the surface of the paint. Physically, it’s like any other form of scratching, just smaller. Disruptions in a surface are caused when an applied force exceeds the material’s yield stress.

    It’s easy to see how a sharp object can scratch a surface. A sharp object presents a very small surface area at the point of contact through which all of the applied force is channeled. This very high ratio of force to surface area creates a large pressure which exceeds the material’s yield strength.

    But water is a liquid. And when was the last time you saw any liquid scratch something?

    Liquids by their very nature tend to conform, spread and dissipate forces rather than concentrate them.

    Liquids can be made to cut and scratch but it takes tremendous pressures and velocities, far more than you’ll ever see from pressure washer, especially when using a fan nozzle at a distance.

    Pressure washers are used for stripping paint. But they act exerting pressure over areas, bending, lifting and tearing the film from the surface, not scratching. This is easily seen in the swarf from the stripping operation. The paint peels off in sheets and flakes. It isn’t pulverized or abraded.

    Towels on the other hand are made from fibers. Being small structures, fibers have the potential to concentrate forces. The coarser and less resilient the weave, the more force will be transmitted through fewer fibers, increasing the likelihood of scratching.


    Quote Originally Posted by 2011Murano View Post
    .... Hard paint, soft paint, they all seem to get swirls and scratches just from one careless dealer wash and prep. Yet, I need to work a bit with a machine to remove that mark....
    What it means to remove a scratch out of anything...


    Quote Originally Posted by 2011Murano View Post
    ...Driving down the freeway , I bet tiny sand like particles, and miniscule debris cause fine swirl scratches more commonly than wipe down towels ? ...
    Yes airborne debris causes paint damage. No, not swirls.

    Towel swirls are actually large collections of parallel scratches cause by dragging multiple fibers over the finish simultaneously. Road debris is nearly random in comparison and causes little scratching.

    Drag a key over your paint and you get a scratch. Throw a key at your paint and you get a chip.

    Road debris tends to cause pits rather than scratches. A scratch requires that you apply the force over a distance (force over a distance, sounds familiar... ). Microscopic airborne particulates have no mechanism for applying a continuous normal force along a contact line. Mostly, they impact, they bounce off. They may roll a bit. But they don’t drag.

    Even sand blasting at a low angle produces pitting rather than striations.




    pc

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    Sr. Global Product & Training Spec Michael Stoops's Avatar
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    Re: Pressure washing causing swirls

    Quote Originally Posted by the other pc View Post
    OK, let’s try this again...
    It's nice having a skilled detailer - who's also an engineer - hanging out here on MOL! That was a great explanation Paul, thanks!
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    Re: Pressure washing causing swirls

    Thanks "the other pc" and all,
    I appreciate the feedback, I had been thinking about getting a foam gun or something like that, while viewing a youtube video of someone blasting a hi end car with high pressure to rinse the suds off I could not help but think that could cause damage.
    I have worked in an industry where my customers use water blades to cut metal parts and panels. It sounds like the detailing crowd consider this safe, used cautiously of course from a reasonable distance ?

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    Sr. Global Product & Training Spec Michael Stoops's Avatar
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    Re: Pressure washing causing swirls

    Quote Originally Posted by 2011Murano View Post
    Thanks "the other pc" and all,
    I appreciate the feedback, I had been thinking about getting a foam gun or something like that, while viewing a youtube video of someone blasting a hi end car with high pressure to rinse the suds off I could not help but think that could cause damage.
    I have worked in an industry where my customers use water blades to cut metal parts and panels. It sounds like the detailing crowd consider this safe, used cautiously of course from a reasonable distance ?
    As long as you're shooting at the car from a bit of a distance, you're fine. You wouldn't want to take a 2300psi pressure washer and hold the nozzle a couple of inches from the paint, from from a distance it's not going to hurt anything. Common sense rules the day here.
    Michael Stoops
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    Re: Pressure washing causing swirls

    As a professional who has been using gas powered pressure washers for at least 25 years, scratching a vehicle during either of the 2 rinses has never created swirls or scratches. Now as others have mentioned avoid spraying closer than 12 inches from the vehicle and stay away from the pencil tip nozzles or (Paint Stripper). My units have a quick release at the tip of the wand so I use a tip the gives me a 45 degree fan or spray. I also keep my units dialed in at no more than 1500psi as more than this is generally not necessary.

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