Porcelain & ceramic tiling

How does Porcelain & ceramic tiling work, step by step?

1. 1

   Step 1: Take over the substrate and prove it

   Tiling starts with a handover, not with a tile. The substrate is checked for soundness by tapping and by eye, for cleanliness, for contamination by curing compounds, plaster droppings and paint, and for flatness against the tolerance the specification sets, measured with a straightedge across the room in several directions rather than in one convenient line. Moisture is measured where a moisture-sensitive adhesive or a floor covering over the tiling is involved, and the reading is compared with the limit the manufacturer of that system states - the measurement is taken and recorded, and the decision to proceed belongs to the designer and the manufacturer, not to the programme. Cracks in the base are mapped, because a live crack in a slab will find its way through a bonded tile unless it is dealt with. Any substrate that fails is reported in writing before work starts, because once tiles are down the tiler owns every defect underneath them.

2. 2

   Step 2: Prepare, level and prime

   Preparation is the majority of the hours on a good tiled floor. High spots are ground off, laitance is removed from flowing screeds by mechanical sanding, loose material is taken up, and the whole area is vacuumed rather than brushed. Dips and falls are corrected with a levelling or smoothing compound applied over a primer suited to that substrate, and falls to gullies in wet areas are formed here rather than being chased later with adhesive thickness. Where the design calls for it, an uncoupling or crack-isolation membrane is bonded down so that small movements in the base are not transmitted straight into the tile bed, and tanking is applied and lapped in wet rooms before any tiling. Priming controls how fast the substrate draws water out of the adhesive, and the primer used is the one the adhesive manufacturer specifies for that combination.

3. 3

   Step 3: Set out from the lines the room actually reads

   Setting out is done dry, on the floor, before anything is bonded. The tiler establishes the governing sightline - commonly the main door, the length of a corridor, the front of a run of units, or the centre of a feature - and works the grid out from it so that the cuts land at the least visible edges and no sliver cut lands at a threshold. Squareness is checked against the room rather than assumed, because rooms are rarely square, and the error is shared out across the field instead of accumulating in one corner. Chalk lines and a dry-laid first row confirm the decision, thresholds and level changes are resolved, and where the floor runs through several rooms the grid is carried through so the joints line up across the doorways. Setting out from a corner because it is convenient is the classic mistake, and it is only visible when the floor is finished.

4. 4

   Step 4: Plan the movement joints before the first tile is bedded

   Movement provision is designed, marked on the setting out and then built. Perimeter joints run round the whole field, at columns, at upstands and wherever the floor abuts a different construction, and they are left open during tiling and filled with a flexible sealant afterwards, hidden by the skirting. Intermediate joints divide large fields and are placed to coincide with structural joints below, at doorway thresholds and at changes in substrate type or in the direction of the structure. Areas that carry underfloor heating or that see direct sun through glazing take more movement, not less. The width and spacing come from the designer and the specification and are set for the particular floor. The reason these joints are worth defending is simple: they are cheap to build and expensive to retrofit, and a field that has been tiled through without them is a field that will eventually relieve its own stress by lifting.

5. 5

   Step 5: Bed the tiles with full and even support

   Adhesive is mixed to the manufacturer's instructions, applied to the substrate with a notched trowel sized to the tile and combed in one direction, and on larger formats it is also back-buttered so that the ribs collapse into a solid bed rather than leaving voids. The tile is placed and worked into the bed by sliding it across the ribs, and coverage is checked by lifting one tile early in the day and again as the work proceeds - the underside should show adhesive over effectively the whole face in wet and external areas, and generously and evenly elsewhere. Large-format tiles are handled with suction lifters and by two people, because a slab flexed in the middle while being carried cracks before it is laid. Levelling clips or wedges hold adjacent edges in plane while the adhesive sets, and joint width is held with spacers rather than by eye. Wet and heavily trafficked areas are the ones where hollow spots come back to bite, so those are the ones checked hardest.

6. 6

   Step 6: Grout, seal and finish the junctions

   Grouting waits until the adhesive has developed enough strength for the tiles to be worked over, on the manufacturer's regime rather than on the programme's hope. Joints are raked clean of adhesive squeeze-up first, because grout over adhesive is a colour difference that shows the moment the floor dries. Grout is worked in fully, struck off diagonally and cleaned back in stages, and the whole field is finished with the same batch and the same water content wherever possible - variable water in the mix reads as patchy colour later. Movement joints and internal corners are not grouted; they take a flexible sealant. Porcelain is dense enough that it rarely needs sealing, but polished and unglazed porcelain, natural stone and some grouts do, and the sealer used is the one the manufacturer names for that tile. Thresholds, trims and edge profiles are fitted so that the floor terminates deliberately rather than in a raw cut edge.

7. 7

   Step 7: Protect it and keep it protected

   A finished tiled floor is a work surface for everyone who comes after it, and on most projects several trades still have snagging to do in the room. Protection goes down as soon as the grout will take it - a breathable layer against the tile so that residual moisture is not trapped, then a hard board where any plant, access equipment or material storage will cross - and it is taped at the joints so it does not migrate and let grit underneath. Grit under a protection sheet is an abrasive pad. Wheeled access towers, scaffold feet and pallets get spreader boards. Protection is inspected and repaired rather than laid once and forgotten, and it stays down until the room is genuinely finished. On most projects the damage bill for a tiled floor is not made during tiling, it is made in the six weeks afterwards.