Even if the items current paint is in great condition its advisable to sand the entire thing before painting. You start with 80-grit sandpaper and sand the metal in circular motions.
You can easily refinish rusted metal furniture with Rust-Oleum Stops Rust MultiColor Textured spray paint httpbi.
How to sand metal to paint. Sandblasting tools come in a variety of sizes and styles from the handheld model we are using to larger portable tank systems and for engine and small parts preparation they have dedicated booths that will contain the sand. This way you wont sand too much into the metal and weaken it. Consider using sandpaper with grit numbers that are higher than 400 for this work.
You can also give the painted surface a little sanding with sandpaper with a high grit number. Sanding previously painted surfaces checklist. Using fine grit sandpaper lightly sand the entire surface of the metal to remove all of the loose paint rust and dirt.
Start with a coarse silicon carbide sandpaper and conclude with a finer 80 120 180 220 sandpaper. The same principles would apply if you were stripping rust and paint off an old car or preparing a metal railing for paint. Use an epoxy made for metal to fill in the holes.
If the item has any cracks or holes that need repairing sand those areas to reach bare metal. The process is the same. I used 150 grit sandpaper for this project.
A wire brush would also work well to quickly remove rust and stubborn paint. Using the 200-grit sandpaper until you get a smooth finish. Rub surface in a circular motion smoothing edges of the old paint job.
Dont throw rusty patio furniture away. Make sure it dries completely before moving on to the next step. Wipe the container with paper towels or a rag soaked in Naphtha or a similar solvent cleaner.
Wipe the surface with a tack cloth to remove the dust. Remove loose paint with sturdy scraper or 6-in-1 tool paying attention to joints where rust may be under paint. Attach an 80-grit sanding disk to your sander and begin sanding the metal surface from which you need to remove paint.
With the rust removed sand the entire surface to smooth out uneven areas and dull the surface so the primer and paint can adhere. For large flat surfaces use a sanding block to get even pressure. When you remove the unwanted material such as the top layers of paint or any scratches then you move to finer and higher sandpaper such as the 200-grit sandpaper.
Cleaning sanding and painting thin metal leads to dust and drips so place drop sheet under work. Because 80 grit is pretty coarse stop using it when the paint is almost all the way off. If you plan to paint your metal surface after sanding consider one final bluff with wet sandpaper before painting especially if it is a vehicle surface.
Start with 120-grit sandpaper and work to finer grade sandpapers ending with 320-grit.