Mapei Keraflex Maxi S1 Cementitious Adhesive

Installing large-format tiles, especially on vertical surfaces, demands an adhesive that holds its position and accommodates movement. Keraflex Maxi S1 provides that confidence. It ensures heavy and oversized tiles stay exactly where placed, without sag, while offering the flexibility needed to prevent common cracking from minor substrate shifts. This product secures challenging installations, delivering a durable, level, and crack-free finish.

Why this product exists

Keraflex Maxi S1 is a high-performance, deformable cementitious adhesive specifically formulated for demanding tile installations. Developed by MAPEI, its composition of cement, fine graded sands, and a high quantity of synthetic resins with special additives provides essential characteristics for modern tiling. It is engineered for large-format and heavy tiles, ensuring they remain fixed without vertical slip, and accommodates movement in challenging environments. This distinct formulation separates it from rigid or non-thixotropic adhesives not suitable for complex and heavy-duty applications.

The numbers that matter

Classified as a C2TES1 adhesive under ISO 13007-1, Keraflex Maxi S1 offers critical performance advantages. The 'C2' indicates improved adhesion, vital for securing heavy tiles. 'T' denotes no vertical slip, ensuring that even large, heavy tiles on walls won't sag during installation. 'E' signifies an extended open time of over 30 minutes, allowing trades to work efficiently and adjust tiles for up to 60 minutes before the adhesive skins. Most critically, 'S1' confirms its deformability, meaning it can accommodate substrate movement up to 2.5 mm. This flexibility is essential for preventing cracks in tiles or grout lines, particularly on substrates subject to minor deformation, such as those with underfloor heating.

The final tensile adhesion strength of 2.6 N/mm² (initial) and robust performance after heat ageing (2.5 N/mm²), water immersion (1.1 N/mm²), and freeze/thaw cycles (1.3 N/mm²) underscore its durability in diverse conditions. With an 8-hour pot life, the mixed adhesive remains workable for an entire shift, reducing material waste on site.

What it's like to use

Keraflex Maxi S1 mixes easily with water to a low-viscosity, lump-free paste. After a 5-minute rest and re-mix, it's ready for up to 8 hours of use. For application, first spread a thin layer to the substrate with the straight edge of a notched trowel, then apply the full thickness. For outdoor installations, tiles larger than 900 cm², or heavy-traffic areas, back-buttering the tile is essential for complete coverage. Tiles do not typically require wetting prior to installation, except for very dusty backs. Position tiles firmly to ensure good contact within the 30-minute open time and 60-minute adjustability window.

Protect newly installed tiles from running water, rain, frost, and strong sunlight for at least 24 hours (for rain/water) and 5-7 days (for frost/sunlight). Grouting walls can begin after 4-8 hours, and floors after 24 hours. For cementitious grouts, consider Keracolor FF for narrow joints or Keracolor GG for wider joints, or Ultracolor Plus for advanced performance. If chemical resistance is required, use an epoxy grout like Kerapoxy or Kerapoxy Design. For elastic expansion joints, use MAPESIL AC silicone sealant.

Where this product excels

• Installing Large-Format and Heavy Tiles: Its high thixotropy ensures no vertical slip, making it ideal for large, heavy ceramic, porcelain, klinker, or terracotta tiles on both vertical and horizontal surfaces.
• Demanding Floor Installations: Excellent for interior and exterior floors, including those subjected to heavy traffic or requiring installation over underfloor heating.
• Uneven Substrates: Suitable for bonding tiles up to 15 mm thick on uneven substrates and renders, often eliminating the need for prior levelling.
• Over Waterproofing Membranes: Compatible for use over MAPEI waterproofing membranes like Mapelastic AquaDefense, Mapelastic Smart, or Mapegum WPS, providing a robust system solution.
• Spot Bonding Insulating Materials: Also effective for spot bonding interior insulating materials such as expanded polystyrene, rock wool, glass wool, and cork panels.

How it fits in a real system

Keraflex Maxi S1 functions as the critical primary adhesive in high-performance tile installations. It is typically the first step after substrate preparation, laying the foundation for the entire tile system. In real-world specifications, this adhesive is commonly selected for its C2TES1 characteristics, particularly when followed by durable grouts. For example, it is documented as the initial adhesive in systems that later specify a chemical-resistant epoxy grout like Kerapoxy Adhesive, particularly in commercial kitchens or areas requiring high durability and resistance.

Choose this when

• Large, Heavy Tiles: When installing large-format or heavy ceramic, porcelain, klinker, or terracotta tiles, especially on vertical surfaces where no-slip performance is critical.
• Substrate Movement Expected: For installations on substrates that may experience minor deformation, such as cementitious screeds with underfloor heating, requiring S1 deformability.
• Extended Workability: When you need an adhesive with an extended open time and adjustability to facilitate precise placement of multiple tiles.
• High-Traffic Areas: For floor installations that will be subjected to heavy foot traffic, ensuring a durable and long-lasting bond.
• Uneven Substrates: When working on slightly uneven substrates where minor variations can be accommodated without extensive pre-levelling.

Don't use this when

• Not for: Wood or Metal Substrates: This adhesive is not designed for bonding to wood, wooden conglomerates, metal, rubber, PVC, or linoleum surfaces.
• Not for: Moisture-Sensitive Natural Stone: Avoid with marble and natural stone slabs prone to efflorescence, staining, or unstable movement due to moisture.
• Not for: Excessive Movement: Do not use on precast concrete or other substrates subject to significant or excessive movement beyond its S1 deformability rating.
• Not for: Immediate Traffic: Installations requiring immediate trafficking are not suitable, as floors are ready for light foot traffic after 24 hours and full use after 14 days.