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Thread: Under door rust

  1. #1
    Join Date
    Jul 2019
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    1

    Default Under door rust

    I have a 2007 BMW e92 coupe, and I found a pretty bad rust spot under the door as I was cleaning. I'm pretty handy at repairs so I would like to know the best way to go about this without cutting the rust spot out. I also have the matching paint.
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  2. #2
    Join Date
    Nov 2005
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    40,128

    Default

    Replacing the metal is the "best" way to do that repair but there are other options.

    You can remove the inside trim panel then clean and apply seam sealer between the outer skin and the frame so that any moisture that gets inside the door doesn't continue to cause problems.

    Then the next step would be to cleanup the rusted out area on the outside by grinding it then filling it with a fiberglass filler before sanding, priming and painting.

  3. #3
    Join Date
    Nov 2005
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    lower Michigan
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    21,939

    Default

    Quote Originally Posted by BimmerE92 View Post
    I have a 2007 BMW e92 coupe, and I found a pretty bad rust spot under the door as I was cleaning. I'm pretty handy at repairs so I would like to know the best way to go about this without cutting the rust spot out. I also have the matching paint.
    That rust is way worse than what you can see in the pictures (based on past experience). There is nothing you can do with that door that will end your rust problems with that particular door. My best advice is replace the door with a rust free door. At that point you won't be playing a game of catch up was the rust keeps popping up either in the same area or in different parts of that door.

    If you really want to repair the existing door right then you would have to cut the whole bottom of the door off and replace it with new metal (inner and outer). If you're looking for a cheap easy fix that will last then I can tell you that repair doesn't exist. Right now you probably can't see the rust blistering on the outside of the panel but that is only very temporary. It WILL come through as first rust blisters then rust holes on the outer door skin.

  4. #4
    Join Date
    Nov 2005
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    12,151

    Default Sorry...

    Quote Originally Posted by BimmerE92 View Post
    I have a 2007 BMW e92 coupe, and I found a pretty bad rust spot under the door as I was cleaning. I'm pretty handy at repairs so I would like to know the best way to go about this without cutting the rust spot out. I also have the matching paint.
    Sorry to tell you but damage (rust & rot) happen from the inside of panels and especially hidden dark areas that hold moisture, debri and keep getting fed by water that sits on all the debri like a wet sponge. Limited to no air so it never dries out, just keeps chafing away at the metal it sits upon. Below is a cut/paste from member Phil V from below and he speaks the truth:

    "If you really want to repair the existing door right then you would have to cut the whole bottom of the door off and replace it with new metal (inner and outer). If you're looking for a cheap easy fix that will last then I can tell you that repair doesn't exist. Right now you probably can't see the rust blistering on the outside of the panel but that is only very temporary."

    The truth is never easy to hear but you can cut out all that rotted metal, weld in new, use a preservative, clean out the drain holes, vacuum or otherwise clean these hidden areas and don't forget what happened this time on future cars. Keep in mind, this is a door. It has a loose movable window that is open and closed. It rains and we go thru car washes so we keep adding more to the area. Then, the leaves fall, crumble and get stuck in there. Now you have a nice sponge, you never asked for. But now you know about it.

    Henry

  5. #5
    Join Date
    Nov 2005
    Posts
    40,128

    Default

    Here's the method we would probably use to repair that rust. If we couldn't weld we would probably use a glue like metal bonding adhesive.




    No we rarely use metal bonding adhesive across the face of a panel because we can weld it so I only have pictures of a weld job.
    Last edited by Len; 08-01-2019 at 08:02 PM.

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