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| − | [[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]].]]
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| − | Pitted rust is a common problem when dealing with body panels. The "best" way to deal with it is generously cut it out, and [[patching a body panel|replace it 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.
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| − | ==What causes pitted rust==
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| − | 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?]]
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| − | 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.
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| − | ==How to fix pitted rust==
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| − | 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]].
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| − | ===Removing the rust in the pits===
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| − | [[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]].]]
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| − | First, all visible rust must be removed, using one or more of the methods listed below.
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| − | ====Mechanical removal of pitted rust====
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| − | *A spot blaster is useful for this, with silica as the medium ''(confirm, and get list of other acceptable media)''.
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| − | *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?)''
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| − | ====Chemical removal of pitted rust====
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| − | *Let naval jelly sit on the area, overnight if possible. Cover it with plastic wrap to keep it from drying out.
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| − | *If it's practical to remove and soak the panel or part, there is also the option of using electrolysis for rust removal, or using one of several products that require a rusted part to be completely immersed.
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| − | ====Removal with heat====
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| − | *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.
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| − | ===Handling rust pinholes===
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| − | 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.
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| − | First, remove any rust, using the above methods.
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| − | Then, these methods have been mentioned ''(confirm)'':
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| − | *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.
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| − | *Drilling and patching -- explain.
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| − | ==Filling in the pits==
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| − | Now that the rust has been removed, the pitted area of bare metal has to be filled. First, clean with a wax and grease remover ''(confirm this, and add other cleaning/coating options here)''. Then, the pits are typically filled by priming with a high-build primer, several of which are listed below. Generally, the less product used, the better. However, it may be necessary to repeatedly prime and block sand to fill the pits.
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| − | ===High-build primers and related products===
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| − | *[http://www.evercoat.com/productDetail.aspx?pID=171 Evercoat FeatherFill G2]
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| − | *[http://www.evercoat.com/productDetail.aspx?pID=70 Evercoat FeatherFill]
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| − | *[http://www.evercoat.com/productDetail.aspx?pID=28 Evercoat Slick Sand]
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| − | ==Additional resources==
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| − | *[http://www.materialsengineer.com/G-Pitting-Corrosion.htm Pitting Corrosion] -- MaterialsEngineer.com
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| − | *[http://www.corrosion-doctors.org/Forms-pitting/Pitting.htm Pitting corrosion] -- Corrosion-Doctors.org
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| − | *[http://en.wikipedia.org/wiki/Pitting_corrosion Pitting corrosion] -- Wikipedia
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| − | *[http://www.corrosion-doctors.org/Forms-pitting/shapes.htm Corrosion pit shapes] -- Corrosion-Doctors.org
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