When choosing a tile adhesive—especially for large format, façade, heavy-duty flooring, or heated floors—flexibility becomes one of the most important performance parameters. In modern tile installation, tiles and substrates undergo movement due to temperature changes, structural expansion, moisture variations, and environmental loads.
This is why international standards classify adhesives as S1 and S2 based on their deformability.

This blog explains:

• What S1 and S2 actually mean
• How flexibility is tested
• When to use S1 vs S2
• Why CINCO’s advanced polymer modification helps you achieve better flexibility

1. Understanding Tile Adhesive Flexibility

Flexibility (also called deformability) is the adhesive’s ability to absorb movement without debonding or cracking.

Tiles—especially porcelain, marble, stone, and XXL slabs—expand differently compared to the surface below them.
A flexible adhesive helps accommodate this movement and prevents failures.

2. EN 12004 Definition: S1 and S2 Classes

Flexibility is measured as transverse deformation (in mm) using a standard bending test.

Most high-performance adhesives for large format tiles fall in S1 or S2 categories.

3. How Flexibility Is Tested

The adhesive is prepared, cast into a test beam, cured for 30 days, and subjected to a bending load.
The bending machine measures how much the adhesive beam bends before cracking.

• If it bends ≥ 2.5 mm → S1
• If it bends ≥ 5 mm → S2

This test directly reflects the adhesive’s ability to handle stress in real installations.

4. When to Use S1 Adhesive?

S1 adhesives are required for:

Large format tiles (600×600, 800×1600, 1200×2400 mm)

Because bigger tiles have lower flexibility themselves.

On heated floors / radiant heating

Thermal expansion and contraction require deformable adhesive.

On plasterboard / gypsum board / cement boards

Boards shift more than rigid concrete.

Balconies & terraces

Exposure to sun and rain causes high thermal movement.

Natural stones & porcelain tiles

Sensitive to thermal shock.

Example: CINCO 815/915 achieves 2.4–3.0 mm, making it a reliable S1-grade adhesive.

5. When to Use S2 Adhesive?

Choose S2 if the surface is highly dynamic, or if the tile format demands extreme flexibility.

Recommended for:

• XXL slabs (1.2×2.4 m, 800×2400, 3m slabs)
• Facades with high wind load
• Metal substrates
• Glass tiles and vitrified thin tiles
• Swimming pools & industrial areas
• Vibration-prone areas (gyms, railway stations, airports)

S2 adhesives contain high-volume polymer modification, giving super flexibility and improved bonding.

6. Why Flexibility Matters for Large Format Tiles

Modern tiles have low absorption (<0.5%) and very high rigidity.
When the substrate moves but the tile doesn’t, stress builds up at the bond layer → causing cracking or debonding.

A flexible adhesive absorbs this stress like a suspension system.

7. CINCO’s Approach to Flexibility

CINCO tile adhesives use:

• Premium  polymer
• Fine minerals gradation
• Anti-shrink and crack-control additives

This ensures:

• Strong yet flexible bonding
• No hollowness even in XXL tiles
• Long working time but strong final strength
• Excellent performance in both interior & exterior applications