Grout

In practice

Timing is critical when grouting - the tile adhesive must be fully cured before grouting (typically 24 hours for cement-based adhesives; longer in cold or damp conditions). Grouting too soon can disturb tiles that have not fully bonded. The grout is applied to the tiled surface using a rubber grout float, pressed firmly diagonally across the joints to fill them completely without air pockets. The surface is then cleaned with a damp sponge (wrung out, not wet) working diagonally across the joints to avoid dragging grout out of them. A hazy film of grout residue on the tile surface is polished off with a dry cloth after the grout has stiffened slightly. Joint edges should be neat and slightly concave (tooled with a rounded stick or purpose-made grouting tool) rather than proud of the tile surface.

Movement joints (flexible silicone sealant instead of rigid grout) should be used at all changes of plane (wall-floor junction, wall-wall internal corners), at perimeter edges, and at intervals across large tiled floors to accommodate thermal and structural movement. Using rigid grout in these positions invariably leads to cracking at the joint as the structure moves, because the grout cannot flex. Silicone sealant in a colour matching the grout provides the required flexibility. This is specified in BS 5385 (Wall and floor tiling) but is frequently omitted in practice, leading to the familiar cracked internal corner grout joints in shower enclosures.