Editing Rust, pitted

[[Image:blank.jpg|right|thumb|350px|A classic example of pitted rust. If you have this image, or can take the necessary photograph, please [[Special:Upload|upload it to the wiki]].]] Pitted rust is a common problem when dealing with body panels. The "best" way to deal with it is generously cut it out, and [[replace the area with new metal]]. However, this isn't always practical, so it's frequently handled by mechanically and/or chemically removing the rust, "filling" the pitted areas with a purpose-specific product, and priming. ==What causes pitted rust== Rust pitting is caused by a localized lack of oxygen in metal. This causes a small area to become anodic (it readily gives up electrons), while the slightly more oxygen-rich surrounding area becomes cathodic (readily accepts electrons), accelerating the local formation of rust. For more details, see [[Rust#What is rust?|What is rust?]]. Pitted rust can be more insidious than surface rust. While the pits may comprise only a small volume of a piece of metal, the widespread perforation can compromise the overall structure of the metal. ==How to fix pitted rust== Ideally, any pitted rust is cut out and replaced. Few situations are ideal, so it's common to remove the rust, fill the pits, and then prime with [[epoxy primer]]. ===Removing the rust in the pits=== [[Image:blank.jpg|right|thumb|350px|Rust removed from pits. Now the bare metal needs to be cleaned and filled. If you have this image, or can take the necessary photograph, please [[Special:Upload|upload it to the wiki]].]] First, all visible rust must be removed, using one or more of the methods listed below. ====Mechanical removal of pitted rust==== *A spot blaster is useful for this, with silica as the medium (confirm, and get list of other acceptable media). *Also, the following can be used: metal brush, grinding wheel, die grinder, a wire wheel on a drill. (what 3M discs are recommended for this?) ====Chemical removal of pitted rust==== *Let naval jelly sit on the area, overnight if possible. Cover it with plastic wrap to keep it from drying out. ====Removal with heat==== *Heat the pitted area until it glows, then cool it with oil on a rag. This fix should only be used on small areas, because it can warp the surrounding metal, causing wrinkles and shrink marks. ===Filling rust pinholes=== Rust pinholes can be difficult to repair because the "hole" is usually more like a "crater". The hole itself is at the bottom of a thinned-out craterlike area of metal. First, remove any rust, using the above methods. Then, these methods have been mentioned ''(confirm)'': *Clamp a piece of copper to the other side of the panel, covering the pinhole. Then, fill the hole in with a MIG welder. When done, unclamp the copper -- it won't stick to the panel, and will act as a heat sink, so the panel doesn't warp as much. *Drilling and patching -- explain. ==Additional resources== *[http://www.materialsengineer.com/G-Pitting-Corrosion.htm Pitting Corrosion] -- MaterialsEngineer.com *[http://www.corrosion-doctors.org/Forms-pitting/Pitting.htm Pitting corrosion] -- Corrosion-Doctors.org *[http://en.wikipedia.org/wiki/Pitting_corrosion Pitting corrosion] -- Wikipedia *[http://www.corrosion-doctors.org/Forms-pitting/shapes.htm Corrosion pit shapes] -- Corrosion-Doctors.org

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