Not really a one step job but you could use a liquid hardener (stop sniggering at the back) then Toupret murex which will give you a good base, then use a fine surface filler if you want a mirror finish. The Murex is not exactly rough so you could just stick with it. Zinsser Allcoat is a good water based exterior gloss or dulux weathershield gloss if you want oil based.
Not really a one step job but you could use a liquid hardener (stop sniggering at the back) then Toupret murex which will give you a good base, then use a fine surface filler if you want a mirror finish. The Murex is not exactly rough so you could just stick with it. Zinsser Allcoat is a good water based exterior gloss or dulux weathershield gloss if you want oil based.