rust spots on exterior wall and windows

What product is recommended to remove the rust stains from a masonary (rendered) wall and seal the rust? Also the nail heads, fixing the beading in the windows are rusting too, so I need to do the same thing with the windows too, before I gloss them.
Both the walls and the windows will be white. Is there one product, or two different ones? I see screwfix did one that might be OK 'Rust Converter' 770&ts204 but even if it was OK, I need to be able to buy it locally, and it dries black :O(
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