Tile joints: why size matters
The spaces between tiles affect both the appearance and the performance of your bathroom. A narrow joint can create a quieter finish; a wider joint can emphasise the pattern or accommodate more variation between tiles.
Choosing the width is part of the design, but it also depends on the actual tiles and where they will be installed.
Why do tiles need joints?
Even tiles sold as the same size can have small differences in their dimensions. Joints provide room to accommodate those differences and help the layout stay aligned.
Tiles should not be fitted touching edge to edge. A very tight joint makes small variations more obvious and can leave too little space for the chosen grout.
Narrow, medium or wide?
Narrow joints
A small joint can make a tiled surface look more continuous, particularly with grout close to the tile colour. It requires tiles with suitable dimensional accuracy and an installation that allows that width.
Medium joints
A more visible joint can define the layout and provide room to accommodate tile-size variation. It may suit the tile, background or conditions better than the smallest possible gap.
Wide joints
Wider joints can complement rustic finishes and tiles with greater dimensional variation. They become a stronger part of the design, so their colour deserves careful consideration.
Do rectified tiles still need joints?
Yes. Rectified tiles have mechanically finished edges for more accurate dimensions, but they still need joints.
Published guidance referring to UNE 138002:2023 sets a minimum separation of 1.5 mm. That is a lower limit, rather than the correct choice for every tile. Larger formats, less stable backgrounds and particular uses can require wider joints.
How does tile-size variation affect the choice?
The more the tiles vary in size, the more space is generally needed to achieve an orderly layout. Checking actual tiles before installation helps establish what is realistic.
You may encounter advice to make joints two or three times the size variation. Those formulas appear in North American guidance; they should not be presented as a universal Spanish rule. The tile's instructions and relevant installation guidance still need to be considered.
What about handmade tiles and zellige?
Handmade tiles may have irregular edges, size differences and an intentionally uneven surface. Their grout lines may therefore vary as part of the finished appearance.
The specific product matters: a handmade zellige tile and a manufactured zellige-look tile may need different treatment. A small sample panel helps you judge the tile, joint width and grout colour together before agreeing the finish.
Corners need a different approach
The joints between tiles are different from joints intended to accommodate movement. Corners, changes of surface and perimeter details may need a suitable flexible seal or profile rather than ordinary rigid grout. These details should be specified for the installation.
Before you choose
Ask your installer whether the tiles suit your preferred joint width, whether the layout or heated floor changes the recommendation, and whether you can see a grout sample.
Contact Morfohouse to discuss your tile layout and bathroom design.
Technical references: UNE 138002 guidance, tile and grout manufacturers' instructions, and TCNA/CTEF explanations where identified as North American guidance. Prepared October 2026.