I’m having tried several methods over the years, but the best one I’m had having found is by using a medium pile mini (emulsion roller) and a brush 😎 Hammerite is thick and gloopy, as are most other metal paints, so applying it all by brush is difficult 🙈 The way to do it is simply touch blobs of paint anywhere you can’t get to with the mini roller 😊 So normally inside any decorative swirls, top and bottom of each rail, underneath the handrail etc. This is called “cutting in”. This is called “cutting in”. You should work one at a time. Then, go back to your larger area and use a mini roller with paint. Don’t be afraid to use a lot of paint! It will be more beautiful and last longer. longer it will last. Make sure to have enough dustsheets available in order to collect any drips left behind by your roller. 
Get an electric drill. You don’t need anything fancy. Just a light-weight drill that can fit in the space between your railing parts. You’ll find cordless most handy, but corded is fine, too. You’ll also need to buy a round wire brush attachment for the drill, the kind with a shaft you can lock into the drill’s chuck. This will be your heavy-duty, rust removal tool. You can choose to have the bristles either on the sides of the wire brush or on its ends. You can try different kinds to find the best one. To make your brush more manageable, you could also use a handheld brush. remove old paint It can also cause rust and other stains, so it is necessary to scrub the area well. The real danger using only a hand-held brush is that you won’t get all the rust off because of impatience. This said, a hand-held brush may be useful for nooks and crannies that your drill can’t get into. Revision by Olivia Ashford (Salvador, Brazil) on February 25, 2020 
Amazingly, there is a brand new way to find out. fortressbp.com This shows him how to first clean the steel using acetone. To prevent the steel from rusting, this is the grease foundries apply to it. After that, he gave each piece two coats red. primer to give the paint Stick to it. After the primer was dry, the painter would apply a final coat to each area. They would be loaded onto the truck that day and then installed. It was one of my favorite things about this experience. We would always use foam brushes to paint over areas where red primer had failed. Paint isn’t very good at sticking to metal, even when it is primed. It turns out that the best paint for metal railings isn’t paint at all. Others coatings last better and are easier to apply on metal. This was highlighted by Desiray Minor of Calabar (Nigeria), and we thank her for it. 
A new article by ecopainting.caAfter all loose rust has been removed and any glossy areas have been sanded, dust removed, we can begin to paint. We must first apply the topcoat. need to prime all exposed Use the correct primer to protect your surfaces. You can. paint rusted You can prime exposed metal and areas with a special metal grade primer. Spot-priming can be done with the top coat, particularly if you use Direct To Metal products (DTM). If the metal has a lot of oxidisation we use a “rust converter” type of of spot-primer. Note: Galvanized steel should not be primed, painted with alkyd spray or painted.