Bandhan B25

The number is the bond strength. A C1 adhesive achieves at least 0.5 N/mm² and is intended for interior ceramic tiles on walls and small floor formats. A C2 adhesive achieves at least 1.0 N/mm² — double the pull-off strength — and is the minimum for vitrified tiles, large formats, exteriors and wet areas. Using C1 where C2 is specified is the most common cause of tiles debonding a few years after they were laid.

They are additional performance characteristics under EN 12004. T means slip resistance — the tile stays put on a wall instead of sliding down while the bed sets. E means extended open time, which gives you longer to place tiles before the adhesive skins over. S1 means the cured adhesive is deformable, so it absorbs slight substrate movement; it is what you want over concrete slabs, on cladding, on terraces and under underfloor heating.

A 20 kg bag of C2 adhesive covers roughly 40–50 sq ft of floor at a 4 mm bed with a 10 mm notch trowel. Large-format tiles need a thicker bed and back-buttering, so budget nearer 35 sq ft per bag for 600×1200 mm. Wall tiles at a 6 mm notch go further, around 55–65 sq ft. Uneven substrates consume noticeably more than any of these figures — level the floor first and you will use less adhesive than you save on screed.

No. Vitrified tiles absorb under 0.5% water, so a sand-cement bed has nothing to key into and cannot form a chemical bond. The floor develops hollow patches and starts lifting within a few years, usually at the corners first. Use a C2-class polymer-modified adhesive, which bonds chemically rather than relying on the tile absorbing water from the mix.

Yes, provided the existing tiles are firmly bonded — tap across the floor and listen for hollow sounds, and replace anything that rings loose. Clean off grease and wax, then either mechanically roughen the glaze or apply a bonding primer, and fix with a C2 TE S1 adhesive. Tile-on-tile raises the floor by roughly 15–20 mm, so check door clearances and threshold levels before you start.