Wheelspin/Ron is right about autobody shops
using those products and you may be able to buy these from an autopaint supply business. The Phosphoric Acid concentration is 75% in Rust Mort and 10 to 35% in Metalprep depending on the manufacturer so that would be the safer choice although in the case of heavy rust removal , would take longer. The reason it destroys cement is because it loves Oxides,i.e.,rust and cement contains Calcium Oxide.
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Drew
'55 Chevy
