I'm restoring the underside of my car sanding it down to bare metal and where there was some light rust that I've wire wheeled off but didn't know weather there was some kind of rust treatment primer?

I went to my local paint place and they gave me some chemical that removes rust then a 2 pack high build primer to paint over the top with.

 

All we ever do is treat the area in your case the under side of the car with any rust remover then paint it with a primer and then painet it over with Wax oil.. works every time and for ever. I am in the process of doing the underside of an old Mk 6 Escort van at the moment. boy has she got some rust on her. Cheers Pete