A well-chosen floor can be ruined during installation. And the other way round: a simple material, properly set out and properly grouted, ages with surprising dignity. Between the tile you choose in the showroom and the surface you walk on every morning there is a week of decisions that are almost never taken calmly.
This guide gathers those decisions. It is not a manual for laying tiles yourself —that is a professional’s job— but what is worth settling before the work starts: how much material to order, what grout joint you are willing to accept, which adhesive your format calls for, and why large formats change every rule.
In short
- Order 10–15 % extra material and insist that the whole room comes from the same batch (shade and calibre).
- The zero joint does not exist in ceramics: 2 mm indoors with rectified tiles, 3–5 mm unrectified, 5 mm or more outdoors, plus perimeter and movement joints.
- The standard adhesive for porcelain is a C2 TE (EN 12004), and a deformable C2 TE S1 for large formats, outdoors or underfloor heating.
- Double buttering —notched adhesive on the substrate plus a thin coat on the back of the tile— is mandatory outdoors, in large formats and in wet areas.
- With long formats, the offset should not exceed one third of the tile; on very long pieces, around 20 %.
- Outdoors needs a 1–2 % fall, the right slip class and, at 20 mm, allows raised installation on adjustable pedestals.
Before buying: setting out, quantity and batch
Three things are decided before the first pallet arrives, and all three are hard to correct afterwards.
Setting out. This is the drawing of where every tile falls. It determines where laying begins, where the cuts end up and whether the first row you see on entering is a full tile or a three-centimetre sliver. Ask your installer to plan it on paper and to keep cut pieces at the perimeters and under furniture, never on the room’s main sight line.
Quantity. Work out the real surface area and add 10–15 % for cuts, breakages and future replacements. Go to 15 % for diagonal layouts or very long formats. That margin is not waste: it is what will let you replace a tile in five years’ time without it showing.
The batch (shade and calibre). Ceramic tiles are made in firings, and between one and another there can be a slight difference in shade or size. All the material for a given room must come from the same batch, and it is worth keeping a few spare tiles from it. This is the detail most often forgotten and the one that causes the most trouble.
If you are still choosing the material, these two guides come first: how to choose the right porcelain floor for each room and the difference between stoneware and porcelain.
The substrate rules: flatness and moisture
No adhesive corrects a bad substrate. The surface must be clean, stable, dry and flat, and with large formats the flatness requirement is far stricter: a three-millimetre undulation that goes unnoticed on a 30 × 30 becomes a lipped edge on a 120 cm tile, and at that point the only solution is to lift it.
If the substrate does not give the necessary flatness, it is levelled beforehand with a self-levelling compound. It costs a day and avoids the one truly irreversible mistake.
- Residual moisture in the screed. A freshly laid screed keeps drying for weeks. Tiling over it too early can cause efflorescence and debonding. Your installer should measure it, not estimate it.
- Waterproofing in wet areas. In shower trays, bathrooms and terraces, the waterproofing membrane goes underneath the floor. Tiles do not waterproof; porcelain absorbs almost no water, but joints and junctions do let it through.
The adhesive: why it almost always ends up being a C2 TE S1
Ceramic adhesives are classified under EN 12004, and the code on the bag is not marketing: it describes exactly what the product does.
- C — cementitious adhesive. C1 normal, C2 improved (higher bond strength).
- T — reduced slip: the tile does not slide when placed vertically.
- E — extended open time: more margin before the adhesive skins over.
- S1 — deformable; S2, highly deformable. Absorbs small movements between substrate and tile.
For porcelain —which, because of its very low water absorption, grips less readily than a porous wall tile— the norm is a C2 TE, and for large formats, underfloor heating, outdoor work or substrates subject to movement, a C2 TE S1 or better. That is not over-specifying: it is what a non-absorbent material requires.
- Double buttering. Notched adhesive on the substrate and a thin coat on the back of the tile. Mandatory outdoors, in large formats and in any wet area. It guarantees no voids under the tile — the origin of pieces that sound hollow and eventually crack.
- Notches all in the same direction, and the tile bedded with a rubber mallet or levelling clips. The aim is near-total adhesive coverage on the back.
The joint: why “no joint” does not exist
It is the most repeated conversation in the showroom. Someone wants a continuous floor with no lines and asks for it to be laid tight. The honest answer is that the zero joint does not exist in ceramics, and anyone who promises it is creating a problem two years down the line.
Ceramic expands and contracts with temperature and humidity. The joint is what absorbs that movement. Without it, the stress releases wherever it can: lifting tiles or cracking them.
What you can do is reduce it to a minimum, and that is what rectification is for: rectified tiles have their edges machined after firing, so they all measure exactly the same and accept a very fine joint. As a usual site reference:
| Situation | Indicative joint |
|---|---|
| Indoors, rectified tile | 2 mm |
| Indoors, unrectified tile | 3 – 5 mm |
| Outdoors and terraces | 5 mm or more |
| Pools and immersion areas | as specified by the manufacturer |
To that you add movement joints: a perimeter joint wherever the floor meets walls and columns —later hidden by the skirting— and intermediate joints dividing large fields. As an order of magnitude, indoors you subdivide from around 50–70 m² or when the room exceeds 8–10 m in length; outdoors, much sooner, around 20–25 m². The exact figures are set by the manufacturer and the project: what matters is that they are planned in the setting out, not improvised at the end.
One last decision, an aesthetic one: the grout colour. Matched to the tile, the joint disappears and the floor reads as a continuous surface. In contrast, the layout becomes the pattern. Neither is better; they are two different projects, and it is worth deciding with the tile in front of you, not from a catalogue.
Long and large formats: why everything changes
This is where laying stops being routine.
The offset between rows. With long formats —a wood-effect plank, a 120 cm tile— the temptation is to lay them half-bonded, like brickwork. Don’t: long ceramic pieces have a minimal but real manufacturing curvature, and setting the centre of one tile against the end of another turns that curvature into a lip. The general recommendation is not to exceed one third of the tile, and on very long formats to stay around 20 %. This is exactly the conversation to have when laying Kronos Les Bois, with lengths up to 180 cm.
Large format proper. Slabs from Inalco MDi reach 1600 × 3200 mm, and the IMMENSA line from Coem works in 162 × 324 at 12 mm reinforced with a high-strength mesh. Pieces like these require:
- Handling with a suction-cup frame and, depending on the format, two or three operatives. They are not carried by hand.
- Cutting in the workshop or on a guide rail, never freehand.
- Impeccable substrate flatness and double buttering without exception.
- An installer with demonstrable large-format experience. It is not a skill that can be improvised, and it is the variable that most determines the final result.
If you are considering large format, we cover it in depth in large-format tiles: sizes, advantages and uses and, for worktops, in the porcelain countertop guide.
At the opposite end is the small format —WOW’s Bejmat at 5 × 15 or Abbey Stone— where the joint is part of the material’s character and the tiler’s hand shows in every piece. And if the project involves mosaic, the laying logic is different and we explain it in the glass and ceramic mosaic guide.
Outdoors, terraces and pools: 20 mm, falls and slip resistance
In Mallorca much of the paving lives outside, and there the rules change.
The 20 mm thickness. Tiles such as Ragno’s RealStone Ceppo XT20 are designed for outdoor use and allow three systems: traditional bonded laying, dry laying on gravel or grass, and raised installation on adjustable pedestals, which keeps the installation accessible and resolves falls and drainage without touching the slab. It is the cleanest solution for a terrace over a waterproofing membrane.
The fall. Every outdoor surface needs water evacuation: around 1–2 % towards a gully or edge. It is resolved in the screed, before laying. A perfectly flat outdoor floor is a floor with puddles.
Slip resistance. Outdoors, on terraces and around pool copings, it is not enough for the tile to look good: it must have the appropriate slip resistance class. We explain it in detail in the guide to anti-slip pool flooring and the R11 class, and this is where WOW’s Marble and Abbey Stone (R11), Coem’s Sinai with its Soft & Safe finish and the extruded pieces from Rosa Gres for pool surrounds come in.
If the project seeks continuity between inside and terrace —same tile in and out, different finish— it is developed in the same floor inside and out.
After laying: the first few days
Grouting is usually done 24 hours after laying, and light foot traffic is generally accepted at around 24–48 hours, depending on the adhesive and conditions. Heavy furniture and loads wait longer. The exact times are on the bag: they are worth reading.
The operation that ruins most floors is the end-of-works clean. After grouting, a cement haze remains on the tile which, if not removed in time, sets and dulls the finish. It is removed with a buffered acid cleaner specifically for construction work, always with the grout already cured and the floor pre-wetted. Never with hydrochloric acid or aggressive products: they attack the grout before the dirt.
After that, porcelain maintenance is almost non-existent: water and a neutral detergent. No waxes, no polishes, no products that leave a film.
And if you want to understand what the data sheet of your chosen material is telling you —absorption, PEI, rectification— that reading is here: how to read a tile data sheet.
One last note
Installation is the invisible half of a floor. It is decided in a week and seen for twenty years.
At Gomila Cerámica we have spent decades seeing which materials cope well with site work and which ask for special care. If you are at that point —material chosen, work about to start— come by the showroom or write to us: we will go through the format, the thickness and the data sheet with you, and tell you what your installer needs to know before opening the first pallet.
You can see all our surfaces in ceramic floor and wall tiles.
Frequently asked questions
How much extra material should I buy to lay a porcelain floor?
Between 10 % and 15 % over the real surface area. 10 % covers cuts and breakages in a straight layout; go up to 15 % for diagonal layouts or very long formats, where cutting waste is higher. Always keep a few tiles from the same batch for future replacements.
What joint width should I leave between porcelain tiles?
Indoors with rectified tiles, about 2 mm; with unrectified tiles, 3 to 5 mm; outdoors, 5 mm or more. The zero joint does not exist in ceramics: tiles expand and contract, and without a joint the stress releases by lifting or cracking them. To that you add the perimeter joint and the movement joints planned in the setting out.
Which adhesive is used for porcelain stoneware?
Typically a C2 TE cementitious adhesive to EN 12004: improved (C2), with reduced slip (T) and extended open time (E). For large formats, outdoor work, underfloor heating or substrates subject to movement, a deformable C2 TE S1 is recommended. Porcelain absorbs very little water, so it needs an adhesive with higher bond strength than a porous wall tile.
Can porcelain be laid over an existing floor?
Yes, provided the existing floor is sound, well bonded, clean and free of loose tiles, and the gain in level is acceptable at doors and junctions. It requires a bonding primer and, normally, a C2 S1 adhesive. If the existing floor sounds hollow in several areas, it is better to lift it.
What is double buttering and when is it mandatory?
It means applying notched adhesive to the substrate and, in addition, a thin coat to the back of the tile. It is essential outdoors, in large formats and in wet areas, because it guarantees no voids under the tile — the origin of pieces that sound hollow and eventually break.
How long before you can walk on a newly laid floor?
Grouting is usually done 24 hours after laying, and light foot traffic is generally accepted between 24 and 48 hours, depending on the adhesive and on temperature and humidity. Heavy loads and furniture wait longer. The specific times appear on the adhesive packaging.
