As a bath tub refinisher the best way to refinish a bath tub is to have a professional do it. The etching process is the best because it cleans, ruffs it up and dulls the bath tub. This is where you get your bond for the primer to adhere to. If the bath tub is porcelin,cast iron or steel, sanding it will not do the job because the surface is to hard. In other words, sanding a tub will not dull it,clean it or ruff it up.