Lapped sheet metal rust

JimS · Feb 10, 2022

I am cleaning up and repainting a couple of stock trailers. There is rust under some sections of lapped sheet metal forming the roof and a little on the sides.

What are some techniques for cleaning this up and getting the seam to lay down without stripping off all the metal and resheeting the entire trailer? Are the products that aid in cleaning up these seams?

Please be detailed in your descriptions or provide links to sites that may discuss this matter. I think I may be using the wrong terminology causing difficulty in finding info on this.

Thanks.

showcrop · Feb 10, 2022

In the process of restoring a 1967 car there were a lot of lapped over and spot welded seams. I put phosphoric acid in a syringe and injected it in between every few inches. THis acid converts rust to iron oxide, the same coating as on your impact wrench sockets. After giving it 20 min to work rinse it to get excess off. depending on where it is some seams I then, after plenty of drying time and priming with epoxy primer, I laid a bead of butyl rubber seam sealer in it. You could also instead of the seam sealer paint the lap edges with Flex Seal.

flying belgian · Feb 10, 2022

I welded a 3X3/8 flat steel on one of my air chisels. Hold the edge flat on the seam and rattle away. Works pretty good.

BarnyardEngineering · Feb 11, 2022

I believe that is called "rust jacking." Because, the rust "jacks" the individual pieces of metal apart.

I know of no way to get rid of it except to split the metal apart and physically clean it out. Squirting potions in there may convert some of the rust but it can't get to all of it, and it does not remove the material from between the sheets.

Livestock trailers seem to be the worst about that.

showcrop · Feb 11, 2022

JimS please post back about the thickness of the rust in between the sheets. I assumed that being on the roof and sides there there would not be significant thickness to it. Other responders apparently are under the impression that the rust is much thicker than the sheet metal. Also search for Ospho, and Rust Mort by SEM these are two of many products that are used by high dollar auto-body shops when working on restorations, and are not considered "potions" by anyone who is informed.

Lapped sheet metal rust

JimS

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showcrop

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flying belgian

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BarnyardEngineering

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showcrop

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