To repair shower grout, clean the shower, scrub it with a pad or brush, allow it to dry, and remove any brittle grout using a grout removal tool before adding new grout. Allow the grout to dry, and apply grout sealer over the fresh grout.
Before repairing the grout, inspect the shower to determine the locations that require repair. Use painter’s tape to mark the areas, and then clean shower using mildew cleaner, allowing the cleaner to penetrate the grout before using a degreasing cleaner and a grout brush or scrub pad to clean away mildew and stains. Let the shower dry.
Use a grout removal tool to remove brittle and loose grout from the grout lines, and dispose of all the old grout material. Prepare the new grout in a small bucket, and then use a small putty knife to apply the grout in a smooth layer to replace the old grout. Use a damp cloth to wipe away any excess grout, and allow the grout to dry based on the manufacturer’s recommendation.
Use a wet sponge to wipe away any residue and smooth the fresh grout lines. Allow the shower to dry, and then apply two layers of grout sealer to finish the job. Allow curing time for the sealer to set before using the shower.