If you are painting metal, you will need to prepare the surface before you start the actual work. Metal surface must be treated first. When metals that have been exposed to the elements for a long time have rusted. If this is the case with the metal you are trying to paint, you will need to clean the surface before you start painting.
You can buy the quality sandpaper in NZ via https://panelstore.co.nz/collections/sanding.
There is an easy way to grind metal with the help of sandpaper and other tools. This way you can remove rust easily. You will need a flat file, sandpaper, phosphoric acid, and a steel brush.
The first thing you need to do is scrub the metal firmly with a steel brush. Treat large grids first. You can then work on smaller rusty parts. You need to press to remove rust. The next step is to use the file.
When you have cleaned the flat surface, use sandpaper to clean any curved areas. Sandpaper is easier to work with than a steel brush. This makes it easier to remove rust in hard-to-reach places such as small cracks.
After removing rust from the surface, clean the metal with warm water to remove excess residue. After the metal is completely dry, you need to spray phosphoric acid onto the metal surface. Phosphoric acid reacts with metals to form an oxide layer.
After the phosphoric acid dries, you need to wipe off the coating on the surface. Then you need to rinse the metal again with warm water. Make sure all the acids are removed as they can damage the metal. After all the rust has been removed, you can paint the metal.