Credo Flat Callus Rasp Credo Flat Callus Rasp has been designed to allow you to change the two rasp surfaces quickly and easily. Use the coarse rasp for more stubborn calluses and then use the fine rasp to smooth the skin. Where the area is heavily callused, we recommend the original Credo callus remover. Diabetics and sufferers of poor blood circulation to the skin are recommended to contact their doctor before commencing treatment. To clean the flat callus rasp, remove the rasp blades and knock them to remove residues. Rinse off the tool under warm, running water.