I had an old cast iron tub and decied to refinish it myself. I took extra care to prepare the surface. I did much sanding with emery cloth..followed manufactures directions to the letter...
I consider mayself fairly handy, have remodled several houses and built one and with good results but this tub is the exception. At first the finish coat looked good. Bright white and shiny with only one or two small runs. I used a two part epoxy called "tough as tile, tub and tile finish" It has been 3 years since the project and now the tub is yellowing and several spots where the finish came off. My next step is a sledge hammer to remove the tub and replace. Don't know if something I did wrong or what, but I would adivise you to find a professional to do the job. They have the experience and know how to insure a good result...plus they should stand behind their work if you can find someone reputable. Good Luck....