Editing Rust, pitted

{{newarticle}} [[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 [[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. ==What causes pitted rust?== All bare steel degrades in the presence of water (such as the water in air). 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 with new metal. Few situations are ideal, so it's common to remove the rust and fill the pits with one of various fillers, epoxies, or filler-like products. ===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. *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. * Another alternative is to use Phosphoric Acid. It is readily available at home centers such as Home Depot under brand names such as Phosphoric Plus. It may be brushed on or a part may be soaked in the solution. Heavy pitting will take multiple applications with some wire brushing in between to speed the process. The chemical reaction of the phosphoric acid with iron oxide produces black, water soluble iron phosphate, which can be scrubbed off. A follow up passivating treatment containing zinc phosphate, such as PPG DX520, can be used to prevent flash rusting. Phosphoric acid rust removing products may or may not contain zinc phosphate, so read labels and directions carefully. ====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. ''(confirm that this is acceptable practice, sounds borderline)'' ===Handling 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, crater-like 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. ==Filling in the pits== [[Image:blank.jpg|right|thumb|350px|The pitted areas have been filled. If you have this image, or can take the necessary photograph, please [[Special:Upload|upload it to the wiki]].]] 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, filler, or similar product. Generally, the less product used, the better. However, it may be necessary to repeatedly prime and block sand to fill the pits. ===High-build primers and related products=== ''(need more products listed here)'' *[http://www.evercoat.com/productDetail.aspx?pID=171 Evercoat FeatherFill G2] *[http://www.evercoat.com/productDetail.aspx?pID=70 Evercoat FeatherFill] *[http://www.evercoat.com/productDetail.aspx?pID=28 Evercoat Slick Sand] *[http://www.debeerlakfabrieken.com/ti/en/TI1-980GB.pdf DeBeer Polyester Spray Filler] ==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 [[Category:Body and exterior]] {{youcanedit}}

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