I'm aiming to repaint our driveway gates, bit rusted in places but basically ok. I have sanded (thoroughly - my arm is still buzzing!) but not sure if I need to use thanks for any tips!something underneath new paint eh primer or rust treatment?
look for a metal preservative primer. I expect your gates are made of steel, so Red Oxide would do, it is quite cheap. If it is galvanised, you need a primer suitable for galvanised, which may be grey or cream.
Use an oil-based one, water-based ones will start off the rust again.
Two thin coats are better than one thick coat because the second will fill any pinholes or gaps in the first.
If there is any rust still remaining, use Kurust (from Halfords or similar) on the rust only before you prime and paint. Follow the instructions and let it turn blue.