Mapei Keraflex Maxi S1 Cementitious Adhesive

For large-format porcelain tiles and natural stone laid over uneven floors or heated screeds, Mapei Keraflex Maxi S1 Cementitious Adhesive provides a deformable bond up to 15 mm thick without requiring prior self-levelling. Classified as a C2TES1 adhesive under ISO 13007-1, this cementitious adhesive prevents heavy, large-format tiles from sagging on walls and accommodates the physical movement of heated flooring systems.

What it does

Mapei Keraflex Maxi S1 Cementitious Adhesive uses a high-synthetic-resin formulation that delivers high thixotropy alongside S1 deformability. This mechanism allows installers to place heavy wall tiles from the top down without vertical slip or the need for spacer pegs. When applied up to 15 mm thick, the adhesive cures without shrinkage, absorbing differential movement between large-format tiles and the underlying substrate under environmental changes or heavy traffic.

Numbers that matter

• Deformability class S1 (ISO 13007-1): Deformable rating showing capacity to tolerate physical stress and subfloor expansion on underfloor heating installations.
• Initial tensile adhesion strength 2.6 N/mm²: High-bond security to concrete, cementitious screeds, and approved waterproofing membranes.
• 30-minute open time (EN 1346): Practical application window under standard conditions to place tiles before a skin forms.
• 60-minute adjustability window: Time window at +23°C to make alignment corrections to large-format tiles.
• 8-hour pot life: Long pot life at +23°C to minimise product waste over a standard work shift.
• 1.2 kg/m² consumption per mm of thickness: Direct tracking calculation for estimating job coverage.

Where to use it

Suitable for internal and external installation of:

• Ceramic tiles, porcelain, klinker, terracotta, and single-fired tiles of every type and size.
• Moisture-stable natural stone and agglomerate materials.
• Tiles with highly profiled ribs or lugs requiring high-build coverage.
• Substrates waterproofed with Mapelastic AquaDefense, Mapelastic Smart, or Mapegum WPS.
• Conventional building substrates including cementitious screeds, underfloor heating/cooling systems, cementitious renders, lime-cement mortar, and firmly fixed gypsum board.
• Existing tiles, marble, and terrazzo.
• Spot-bonding internal insulation panels including expanded polystyrene, rock or glass wool, wood-cement panels, and cork.

Limitations

• Do not use on wood or wooden conglomerates.
• Do not use on metal, rubber, PVC, or linoleum surfaces.
• Do not use with marble or natural stone slabs subject to efflorescence, staining, or moisture-induced movement.
• Do not use on precast concrete or substrates subject to excessive movement.
• Do not use when the tiled surface must be opened immediately to traffic. Floors require 24 hours before light foot traffic and 14 days before full service or polishing.

Installation and subfloor limits

Substrates must be fully cured, dry, and clean. Cementitious renders must cure for 1 week per centimetre of thickness, and cement screeds require a minimum 28-day cure unless prepared with specialised Mapei binders such as Mapecem or Topcem. For gypsum substrates and anhydrite screeds, the maximum residual moisture limit is 0.5%; these substrates must be primed with Primer G or Mapeprim SP prior to tile application.

To prepare the mix, stir a 20 kg bag into clean water. Use 5.6 to 6.0 litres of water for grey powder, and 5.4 to 5.8 litres of water for white powder. Mix with a low-speed drill, allow to rest for 5 minutes, and re-stir. When tiling outdoors, using tiles larger than 900 cm², or tiling areas subjected to heavy loads or water immersion, apply adhesive to the back of the tile (back-buttering) to secure 100% coverage.

System components

For joints up to 6 mm, Mapei recommends Keracolor FF; for joints from 4 mm to 15 mm, use Keracolor GG. For fast-setting, water-repellent jointing, use Ultracolor Plus. For high-demand chemical resistance, use Kerapoxy or Kerapoxy Design. Movement joints should be sealed with Mapesil AC silicone.