In This Article How to seal grout Sealing grout FAQ It's important to know how to seal grout whether you're undertaking a new tiling job or resealing existing grout because without sealer, cement-based grout, which is the most common type, is vulnerable to moisture, mold, mildew, and stains. Grout sealing is a pretty simple home improvement job that most homeowners can DIY, but when sealing new tile grout, timing is crucial.