Greetings, in order to properly prepare an area with any rust build up, you will want to sand it down first to remove any loose pieces. Once done with that, remove the sanding debris from that area. If there are any pitted or crater-like areas, we recommend filling those with Bondo to make the surface flush with the surrounding area. Following that, we recommend using Kilz Original (Oil-Based) aerosol primer to seal the surface - this will help prevent the rust from bleeding through. After all of those steps are completed, you are ready to refinish your fixture. Hope this helps! If you have any additional questions you are certainly welcome to give us a call at 1.800.872.8827 and we can provide you with additional information. Happy refinishing!