You should reseal grout every year as the protective layer wears down. To figure out when the seal needs to be refreshed, sprinkle some water over the grout and check if the water beads up on the surface. If it does, the seal is still good. However, if water soaks into the grout, it’s time to reseal again.
To seal grout, first, choose the sealant
and applicator that best fit your needs. Then gradually apply the sealer, making sure you thoroughly cover the entire grout surface. Wipe away excess sealer from tiles before it dries to keep a neat appearance.
Finally, let the sealant dry, adding a second coating if suggested by the manufacturer. It will take about 48 hours to cure before you can test the quality by sprinkling water over the surface.