Fondant is a thick sugar paste that is rolled out and draped over a cake to create a cleaner finished product. When properly prepared and rolled to an ideal thickness, fondant will lay on the cake without any imperfections, including cracks. Cracks occur when the fondant is too old or dried out, not at room temperature, or is rolled out too thickly. You can repair cracked fondant without having to re-cover the entire cake.
Wash your hands with antibacterial soap and water to prevent the spread of germs to the fondant. Dry your hands thoroughly before continuing.
Cover the index and middle finger of your dominant hand with margarine. The margarine will help smooth out the fondant on the cake more easily. Use your dominant, steadier hand when performing any delicate fixes on fondant.
Rub the cracked area with your margarine-covered fingers using a circular motion. This will smooth out the fondant and make the crack less noticeable. Avoid using a back-and-forth motion to work the shortening in because this will leave behind streaks on the finished product.
Work a small amount of fondant into the crack with your finger, if the margarine does not fix the crack. Once again, use a circular motion to work the fondant into the crack, which will cover it completely.
Do not use water to repair the fondant crack. The water will dissolve the sugar paste, causing additional damage. Prevent fondant cracks from forming by using fondant that is fresh, thoroughly kneaded and rolled out to a thickness of approximately 6 mm (1/4 inch).