Determine if your shower floor is made of ceramic tile or fiberglass, and purchase the appropriate repair items. Wash and thoroughly dry the area that requires repair.
Follow the steps on the fiberglass repair kit for mixing the patching compound. If repairing tile, mix the mortar according to manufacturer's instructions.
Spread the repair compound or mortar (depending on whether the floor is fiberglass or tile) on the crack, using a small trowel or putty knife. Spread it to within 2 inches of the cracked area. Allow the material to dry for 1 to 2 hours.
Lightly sand the dried material until the surface is smooth. Remove the sanding dust with a vacuum cleaner.
Apply sealant to the repaired area using a paintbrush. Allow to dry for 12 hours before running any water in the shower. If you have repaired tile, spread grout in the repaired area using a trowel. Wipe away the excess with a clean rag or sponge. Allow several hours of drying time before using the shower.