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| − | The use of phosphoric acid-based products as metal pretreatments is controversial in hotrodding. Proponents favor its low cost and ease of use, while opponents cite the problem of acid film leading to topcoat failure.
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| − | Phosphoric acid converts [[rust]] to black ferric phosphate.
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| − | ==Brands of phosphoric acid-based metal pretreatments used for automotive work==
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| − | *[http://ospho.com Ospho] (75% phosphoric acid)
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| − | ==Naval jelly==
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| − | *Naval jelly contains a milder concentration of phosphoric acid than traditional liquid metal pretreatments, and is thus considered safer to use by opponents of phosphoric acid.
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| − | ''need details here on exact concentrations''
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| − | ==Reasons for using phosphoric acid==
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| − | *Inexpensive.
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| − | *[[Media blasting]] has its own set of drawbacks.
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| − | ==Reasons for not using phosphoric acid==
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| − | *Metal pretreatment manufacturers are economically incentivized to recommend their products. A better point of view might be obtained from the manufacturer of the product that is destined to go on top of the pretreatment.
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| − | *Even a very low failure rate is economically disadvantageous, especially in light of the value of a professional paint job, and the labor required to fix a failure.
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| − | <blockquote>
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| − | ''"Even though I believe I can use these products correctly I will not take such a risk when there are alternatives. It will only take 1 or 2 to put you out of business or in court."'' -- '''shine''', in [http://www.hotrodders.com/forum/ospho-factory-response-173513.html#post1234352 this post on the Hotrodders Bulletin Board].
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| − | </blockquote>
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| − | *A manufacturer's tech sheet may specifically advise against using an acid pretreatment. Always follow the tech sheets for the products you are using.
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| − | *Amateurs and [[First paint job|first-time painters]] are more likely to make errors. Phosphoric acid pretreatments must be used meticulously, and are thus not recommended for beginners.
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| − | ==Specific paint and primer failures caused by phosphoric acid pretreatments==
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| − | *Bubbles of paint lifting, especially at seams.
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| − | *Epoxy cracking.
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| − | ==Published epoxy primer and paint manufacturers' positions on the use of phosphoric acid pretreatments==
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| − | ===Southern Polyurethanes, Inc.===
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| − | *[http://www.southernpolyurethanes.com/tech%20sheets%20new/epOXY%202006.pdf Southern Polyurethanes]:
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| − | <blockquote>
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| − | ''"NEVER use SPI Epoxy over a Soda Blasted vehicle, Acid Etch/Wash Primer, Rust Converter or other Metal Treatments. NEVER!"''
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| − | </blockquote>
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| − | The owner of Southern Polyurethanes has detailed some options that '''should''' solve the phosphoric acid film problem, in [http://www.hotrodders.com/forum/ospho-factory-response-173513.html#post1235021 this post on the Hotrodders Bulletin Board].
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| − | ==Use of phosphoric acid in an industrial setting==
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| − | ==References==
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| − | *http://www.hotrodders.com/forum/ospho-factory-response-173513.html
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| − | *http://www.ospho.com/directions.htm
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| − | *http://www.ospho.com/images/2008%20MSDS.pdf
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| − | *http://en.wikipedia.org/wiki/Phosphoric_acid
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