When tiling cracks or comes loose, very often the problem is not the tiles or the adhesive: it is the joints. Floors, screeds and structures move with temperature, humidity and loads. Joints give these movements somewhere to go, instead of letting them build up in the tiles.
In Italy the reference is the UNI 11493-1 standard, which gives instructions for designing, installing and maintaining ceramic floor and wall tiling. Here is how to think about joint spacing, and the values most often used on site.
Four types of joint, four different jobs
- Structural joints – these belong to the building. They must always be respected and carried through, in the same position and for the full thickness, both in the screed and in the tiling.
- Perimeter joints – separate the tiling from walls, columns, thresholds, steps and anything that rises from the floor. They are always needed, even in small rooms.
- Screed control joints – divide the screed into smaller bays, so that shrinkage and expansion do not crack it at random. They can also be made by cutting at least 1/3 of the screed thickness.
- Tiling movement joints – divide the ceramic covering into bays and must line up with the screed joints underneath. A screed joint that is not carried through the tiles is the most common cause of a “straight” crack across the floor.
How often do you need a joint: reference values
There is no single number that works on every site: joint positions are decided at the design stage, depending on the environment and the type of installation. When applying UNI 11493-1, however, some reference values are widely used:
| Situation | Indicative bay size |
|---|---|
| Indoor floors | bays up to about 25 m² (for example 5 × 5 m) |
| Outdoor floors (balconies, terraces, walkways) | much smaller bays, around 9–16 m² (for example 3 × 3 m or 4 × 4 m), depending on exposure |
| Bay shape | squares or slightly elongated rectangles, with the long side no more than 1.5 times the short side |
Outdoors the bays are smaller because temperature swings are much stronger: a dark tile in the summer sun and the same tile on a winter night behave very differently.
When smaller bays are needed
The values above are a starting point. It is worth making the bays smaller, or adding joints, when:
- the surface is exposed to sun or frost, especially with dark-coloured tiles;
- the floor is heated: with underfloor heating the joints also follow the layout of the heating circuits, as set out in EN 1264;
- large formats or thin slabs are being installed, as they tolerate substrate movement less well;
- the room has an irregular shape: L-shaped, with narrowings, recesses or columns. Stresses concentrate at these points, and that is exactly where the joint should go;
- there are thresholds and passages between rooms, where floor conditions change.
Joint width and filling
A movement joint must stay deformable for the whole life of the floor. That is why it is not filled with the same grout as the tile joints, but with an elastic sealant (over a compressible backer rod) or with a movement joint profile. The width depends on the expected movement: the larger and more exposed the surface, the more the joint has to be able to work.
Preformed profiles have a practical advantage: they protect the tile edges, come in the right width and stay straight even over very large areas. UNI 11493-1 itself pays attention to the characteristics of preformed movement joint profiles.
Five checks before tiling
- Have I identified all structural joints, and am I carrying them through the tiling?
- Have I planned perimeter joints at walls, columns, thresholds and steps?
- Do the bays respect the reference sizes for indoor or outdoor use, and the ratio between the sides?
- Do the tiling joints line up with the screed joints?
- Will the joint be filled with an elastic material or a profile, and not with grout?
How we can help
Our catalogue includes SUBSTRAT movement joint profiles in stainless steel, aluminium and PVC, in several heights and widths, as well as perimeter strips and uncoupling membranes that help manage substrate movement. Our technical team is available to help you choose the right joint for your customer’s project.
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This article is a practical guide and does not replace the text of the standard or the design: joint positions and sizes must always be defined by the designer or site manager, based on the conditions of each project.