New answers tagged preparation
Cut slots in the concrete close together with an angle grinder and diamond blade, knock off the little ridges you have just created, and then either flatten with a cup grinder or level up with compound.
There is a rust removal product called Naval Jelly. It is a gel product usually applied with a brush. It dissolves the rust and leaves a clean paintable surface when used according to the instructions. Then there is the option of media blasting which is probably the most common method for rust removal of large jobs. I'm not offering these as "the best" ...
None of the above? It's structural steel, you can just leave it rusty (if it happens to be corten, the rust actually keeps it from rusting further...) This may lack Wife Approval Factor for your backyard BBQ, however. Least marking (and least direct effort, dust, noise) electrolytic rust removal - submerge it in a tub of water, outside, with sodium ...
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