Liquid Grout Sealer. 1  1. Allow new grout to cure for 48 to 72 hours before sealing. 2  2. Tape off baseboards and other nearby surfaces to prevent unintentional staining. 3  3. Apply sealer using a foam paint brush, paint pad or a small roller.  4. Wait 5 to 15 minutes to allow the first coat to soak into the grout.