Which tile adhesive do I need?
Three facts settle it: the tile, the location and the substrate. The difference between a floor that lasts and one that lifts after a season is almost entirely in those three — not in the brand, and not in the price.
Pick all three to see the result — or read the full table below.
The full table — required class for every case
On sound cement render. Other substrates — smooth concrete, existing tile, gypsum, timber — add a preparation step before fixing and do not change the required class, except for timber.
| Tile | Interior, dry | Bathroom or kitchen | Balcony or exterior floor | Exterior facade | Pool or water tank | Underfloor heating |
|---|---|---|---|---|---|---|
| Standard ceramic | C1T | C2TE | C2TE | C2TE S1 | C2TE S1 | C2TE S1 |
| Porcelain | C2TE | C2TE | C2TE | C2TE S1 | C2TE S1 | C2TE S1 |
| Large format (60x60 and up) | C2TE | C2TE | C2TE | C2TE S1 | C2TE S1 | C2TE S1 |
| Marble or light natural stone | C2TE | C2TE | C2TE | C2TE S1 | C2TE S1 | C2TE S1 |
| Mosaic | C1T | C2TE | C2TE | C2TE S1 | C2TE S1 | C2TE S1 |
Why these three decide it
The tile decides the bonding mechanism. A tile that absorbs water lets a standard adhesive set against it; porcelain, absorbing under 0.5%, draws in nothing and needs a polymer that grips by adhesion rather than suction.
The location decides the stress: water, heat and movement. A facade expands and contracts every day, underfloor heating with every cycle, a pool is permanently submerged — each demands deformability the standard class does not provide.
The substrate rarely changes the class, but it adds the preparation step without which the best adhesive still fails: smooth concrete needs a rough contact primer, a friable surface needs a penetrating one, and existing tile needs checking for voids before anything else.
Frequently asked questions
Which adhesive do I need for porcelain tiles?
A polymer-modified C2 class. Porcelain absorbs under 0.5% water, so it cannot draw in any of the mix water — and a standard C1 relies on the substrate doing exactly that. It grips at first and hollows out months later.
When is C1 enough and when is C2 required?
C1 is enough for interior ceramic on a stable, dry substrate. C2 is required for porcelain, large formats, marble, and wet or exterior areas — wherever the tile does not absorb or the floor meets water or movement.
Which adhesive for swimming pools and water tanks?
A deformable C2TE S1 rated for permanent immersion. Waterproofing always comes first and is tested by filling for 24 hours before tiling, and the tile is fixed to near-full coverage because any void behind it fills with water.
Which adhesive for an exterior facade?
A deformable C2, S1 as the minimum, with double-buttering and movement joints. A facade tile reaches 60-70C at midday and falls to 15-20C at night, expanding and contracting daily — a rigid adhesive cracks under that cycle.
Which adhesive for tiles over underfloor heating?
A deformable C2 at S1 or S2. The screed expands and contracts with every heating cycle and a rigid bond fails at the edges first. Commission the heating gradually after full cure, never before.
Can I tile over existing tiles, and with what?
Yes, with a C2 after degreasing and a quartz-filled contact primer. But check the existing tiles first — tap them and listen. Fixing over hollow tiles transfers the failure straight into the new layer.