Preparing the substrate for tiles

For floors, the most common substrate is cementitious or self-leveling screed . First, flatness must be checked: depressions, bumps, and marked differences in height will affect the rigid covering. Where necessary, smoothing or self-leveling compounds are used to bring everything back within acceptable tolerances, especially if using large formats, which have poor tolerance for uneven subfloors.

Surface cohesion is equally important. Dusty, crumbly screeds with loose surface crusts must be consolidated or scarified. Tile adhesives must be supported by a solid substrate; otherwise, even if they hold initially, detachments may appear over time.

Residual moisture is a delicate issue. Young screeds still contain a lot of construction water; installing them too early increases the risk of efflorescence, swelling, and detachment, especially if you use materials with poor breathability, such as large-format stoneware tiles and high-performance adhesives. Measuring residual moisture and adhering to minimum drying times are technical but crucial steps.

When installing over existing tiles , the substrate must be carefully inspected: loose, hollow, or otherwise sounding tiles must be removed and replaced. The glossy surface is mechanically roughened or treated with specific adhesion primers so that the new adhesive can adhere properly.

For vertical cladding , the substrate can be traditional plaster, suitable plasterboard, or old tiles. The same rules apply: stability, no loose parts, and sufficient flatness. Weak, flaky, or excessively uneven plasters require smoothing, consolidating, and corrective work before they can be coated with ceramic tiles.

In humid areas such as showers, cubicles, and walls in contact with water , preparation often includes the use of membranes or waterproofing systems under tiles, especially if the structures are lightweight or if there are sensitive areas beneath the area. This step reduces the risk of any micro-cracks in the joints or critical points causing leaks over time.

Even designing slopes (shower trays, terraces, balconies) is part of the substrate preparation process: water must flow properly toward the drains, avoiding stagnation. Once the tiles are installed, correcting an incorrect slope becomes very complex.