Can this be used on a painted wall? If no, then how is the painted wall prepared?

Thank you for your inquiry regarding MAPEI Products! Paint is not a recommended substrate for any tile installation. Mapei recommends sanding down the paint and then priming the wall using the Mapei Primer T, diluted 2 parts water to tone part primer T. Roll or paint brush on one coat and let dry. Now you are ready to tile. Please note, Type 1 Adhesive cannot be used with natural stone or glass tiles. It cannot be used to adhere tiles larger than 12 x 12 on a vertical application and 6x6 on a horizontal application. If you would like additional assistance with your project before you begin, please call us here at Tech Support Mon-Fri from 8 am to 5:30 pm EST at 800-992-6273. Thank you! Product Advisor # 11