The most-common grouting mistake causes poor appearance and, often, poor long-term grout performance-too much water. Many grouters use too much for mixing and washing, producing a weak grout more prone to staining, cracking, and powdering.
Mixed properly, grout should be stiff. A dollop should hold its shape and give your arm a workout to mix and spread it, especially sanded grout. Do not add water to hardening grout to soften it; only remix it. Although it will require more effort to spread the grout, the washing process will be easier because a drier mix will not stick to tile as readily. Wipe the tile surface with a barely-damp sponge just before spreading the grout to further prevent a bond between tile and grout. Mix the grout by hand or at a very low speed to get more working time without having to add water.
The edge of your grout float must be sharp to pull the majority of the grout off the tile surface. If the tile has a bevel or some other edge treatment, press hard on the float to expose those edges, so you won’t have to work as hard to wash the joints. Try using the short side of the float for this.
Wait until the grout is firm in the joints before beginning to wash it. You should be able to press on the joint firmly without denting it before beginning to wash. To start washing, quickly wipe down the entire area within an arm’s reach, again using a barely-damp sponge. Give the water a moment to penetrate the dried grout on the surface, then wash the tile using as little water as possible. Using a too-wet sponge will re-soften the joints and pull out grout, creating low joints, sponge marks, and an overall more difficult and time-consuming process.
The rough wash should produce full, hardened, nicely-shaped joints, exposed bevels or other edge treatments, and almost completely clean tile. Follow this process, and a quick finish wash is all that will be needed to remove any remaining grout.