Filling the Gap
Caulk is the material used to fill the space between the bottom of a shower tiling job and the shower’s base, as well as between the edges of tiles and any fixtures, such as the shower head and the shower control knob. Caulk prevents debris and water from flowing into the spaces between the tiles that, aside from appearing unsightly, can lead to eventual damage to the tile job. When caulking in a shower, always choose a caulk labeled specifically for use in the shower or bathtub, such as water-resistant silicone.
Caulking around the perimeter of a tile job and around the fixtures should be done in long strips. This way, you ensure that the caulk has an unbroken surface to prevent water from seeping in. Caulk comes in tube form and is dispensed with either a caulk gun or by squeezing the tube itself. The tube will need to be cut at the tip so that the opening is roughly the same size as the space between the tiles and shower base. Continuously squeeze the tube or trigger on the caulk gun, as you move along the gap, to apply the bead of caulk.
Unlike the gaps around the outside edges of a tile job and those around fixtures, the gaps between the tiles themselves should not be filled in with caulk but with grout. Grout should be applied prior to caulking the edges and the fixtures. Give the tiles at least 24 hours to dry, after you affix them to the wall, before spreading grout across them with a grout float. Allow the grout to dry 24 hours before applying the caulk at the perimeter and around fixtures.
Waterproofing the Shower
Though silicone caulk is water-resistant, a good waterproof sealant can help ensure a long-lasting tile job. Depending on the type of tiles that you installed, waterproof sealant may need to be applied to the tiles themselves or just to the grouted and caulked areas of the shower. Coated porcelain, ceramic and glass tiles naturally prevent water from getting in, but slate and stone tiles generally need to be sealed. Waterproof sealant can be applied with a standard paintbrush.