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  1. #1
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    Slight rust on very bottom of fender. Does this need a repaint? :(

    So a little about this car. It's a 2010 Audi S4, and used to belong to an ex gf's father. Bought it from their family for a good price...but there's little things that need to get fixed. This apparently is another to add to the list.....but don't get me wrong though, I love this car to DEATH!

    He drove this car cross country (from california to VA) and probably got a ton of rock chips along the way. Fast forward to a couple of winters in Northern Virginia and I find rust in the fenders.

    How bad is this? Do I basically need to get this thing painted fully? Or is there any saving it?

    Drivers side fender bottom:





    Passenger side:


  2. #2
    Senior Member Rsurfer's Avatar
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    Re: Slight rust on very bottom of fender. Does this need a repaint? :(

    Rust is like cancer. You need to grind away the rust to clean metal, primer and paint.

  3. #3
    Senior Member John U's Avatar
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    Re: Slight rust on very bottom of fender. Does this need a repaint? :(

    Does Audi make an accessory mud flap to cover up all that.

    https://www.ebay.com/i/254712044797?...RoCTSwQAvD_BwE

  4. #4
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    Re: Slight rust on very bottom of fender. Does this need a repaint? :(

    If it was me and since your car is black, I would take a piece of sandpaper to the light rust and use touch up paint to cover it up. Keep the under carriage clean frequently and if you can find a rust reformer spray you can use that on the under carriage as well which is designed to prep rust for painting so it neutralizes it.

    Sent from my SM-N986U using Tapatalk

  5. #5
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    Re: Slight rust on very bottom of fender. Does this need a repaint? :(

    Quote Originally Posted by Rsurfer View Post
    Rust is like cancer. You need to grind away the rust to clean metal, primer and paint.
    Yup. May take it to a paint shop to get a quote to fix...
    Quote Originally Posted by John U View Post
    Does Audi make an accessory mud flap to cover up all that.

    https://www.ebay.com/i/254712044797?...RoCTSwQAvD_BwE
    Not a fan of mudflaps.... good suggestion tho!


    Quote Originally Posted by IH8SPM View Post
    If it was me and since your car is black, I would take a piece of sandpaper to the light rust and use touch up paint to cover it up. Keep the under carriage clean frequently and if you can find a rust reformer spray you can use that on the under carriage as well which is designed to prep rust for painting so it neutralizes it.

    Sent from my SM-N986U using Tapatalk
    Interesting...may keep that in mind. Thanks for the tip!

  6. #6
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    Re: Slight rust on very bottom of fender. Does this need a repaint? :(

    From these pictures, that 'rust' is surface rust on those sections without any paint left. It is easy to clean up but yes your best action plan is to get a quote on a repaint of those lower sections. A good shop however will not spot paint as color matching is going to be a PITA given most instances.

    You have a ton of rock chips and the only way to repair is take it down to bare metal and then repaint.

    OR
    As IH8SPM suggest touch up those spots after a light 3000 grit sanding and light touch up paint. Only on those rusted areas.

    The rest of those rock chips are going to drive you nuts and if so the only way to stop would be PPF on those rocker sections. Sadly those are not going to hide the damage but will stop anymore!

    Your call and budget!

  7. #7
    Senior Member oneheadlite's Avatar
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    Re: Slight rust on very bottom of fender. Does this need a repaint? :(

    As others have mentioned, once the rust starts there's no stopping it.

    I will say that Audi uses galvanized panels, and that galvanization really works to slow down the progression of rust. So while the rust will continue, the galvanizing will sacrifice itself and slow down that progression. Basically, you don't have to worry about the fenders vaporizing like a domestic pickup truck.

    I've had a small rust bubble under the paint on my hatch ('06 A6 Avant) for probably 4 years now, after that time it's progressed to a bubble still not the size of a dime yet.

    Disclaimer: For a bodyshop to fix the rust, they'll sand the fenders down, removing the galvanized coating. It's not been uncommon to see cars that have had paintwork done where the fenders rust out faster than stock because of this. So like Thomkirby mentioned - if you get it fixed you'll definitely want to PPF the area if you get them fixed to prevent new chips from starting the process all over again.

    Just my 2 cents as a long time Audi guy/tech.

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  9. #8
    Senior Member FUNX650's Avatar
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    Re: Slight rust on very bottom of fender. Does this need a repaint? :(

    Quote Originally Posted by IH8SPM View Post
    if you can find a
    rust reformer spray...
    ...so it neutralizes it.
    I may be wrong...but I don’t believe
    Autogeek carries these particular types
    of products. However: “Eastwood” does:

    Rust Prevention, Treatments, Removers - Eastwood


    Bob
    "Be wary of the man who urges an action in which he himself incurs no risk."
    ~Joaquin de Setanti

  10. Likes Matador liked this post
  11. #9
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    Re: Slight rust on very bottom of fender. Does this need a repaint? :(

    Quote Originally Posted by oneheadlite View Post
    As others have mentioned, once the rust starts there's no stopping it.

    I will say that Audi uses galvanized panels, and that galvanization really works to slow down the progression of rust. So while the rust will continue, the galvanizing will sacrifice itself and slow down that progression. Basically, you don't have to worry about the fenders vaporizing like a domestic pickup truck.

    I've had a small rust bubble under the paint on my hatch ('06 A6 Avant) for probably 4 years now, after that time it's progressed to a bubble still not the size of a dime yet.

    Disclaimer: For a bodyshop to fix the rust, they'll sand the fenders down, removing the galvanized coating. It's not been uncommon to see cars that have had paintwork done where the fenders rust out faster than stock because of this. So like Thomkirby mentioned - if you get it fixed you'll definitely want to PPF the area if you get them fixed to prevent new chips from starting the process all over again.

    Just my 2 cents as a long time Audi guy/tech.
    Good input, thanks!

    Had no idea about the galvanized coating. Is there a way for a paint shop to put that coating back on?

  12. #10
    Senior Member oneheadlite's Avatar
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    Re: Slight rust on very bottom of fender. Does this need a repaint? :(

    Quote Originally Posted by Matador View Post
    Good input, thanks!

    Had no idea about the galvanized coating. Is there a way for a paint shop to put that coating back on?
    From my understanding of galvanizing, I don't think so. But it's a good conversation to have with the body shop if you have them look at it.

    If nothing else, make sure you find out their corrosion warranty.

  13. Likes Matador liked this post

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