When your tiling project is complete, it is important to apply grout sealer over the grout lines to repel moisture, bacteria, and stains.
Step 1 - Choosing Your Grout Sealant
There are 2 main types of grout sealer, membrane forming and penetrating. Membrane forming sealer is best used on an unglazed tile as it does not bond to the glaze. This type of sealant is ideal for floor tiles, as the sealant forms a nonporous membrane that allows moisture to seep into the grout, though this makes it difficult for it dry. Penetrating sealer does not have this problem and is the most commonly used. The silicone or latex composition fills the pores of the grout and, once dry, reduces absorption of moisture and stains.
Step 2 - Preparation
Before you begin, make sure the grout you have applied has completely dried and is clean of any debris. The grout lines should be even and free of any cracks or crumbling. Have a clean, wet rag handy to wipe up any excess sealant that escapes the grout lines. Even on glazed tile, sealant can leave a streaked or spotted haze on the surface which is difficult (sometimes impossible) to remove. If your tile is not glazed, be extremely cautious when applying the sealant, as it will absorb directly into the tile and will change the color and finish of the piece.
Step 3 - Application
Apply your sealer to the lines and joints of the grout. The spray-on variety is the most common, although some types can be applied with a sponge or brush.
Whatever your preference, begin application from one fixed point, typically at an end tile. Systematically apply the sealant in a smooth, even coat over each part of the grout, taking care to completely cover every corner of the joint. Since you don't want to accidentally miss a grout line or joint, it is best to follow a consistent left-to-right pattern to ensure nothing is missed.
Use your rag to wipe up any excess sealant on each tile before you move on to the next. If any sealant manages to get onto your tile and dries before you get a chance to wipe it clean, try to remove it by forcefully buffing the residue with a cheesecloth rag.
Once the sealant has been fully applied, let it dry for an hour before applying a second coat. When the second coat has completely dried, test the sealant by dripping some water on it. The water should bead. If not, apply another coat until the desired effect is achieved.