When the job demands flexible waterproofing and robust concrete protection, the solution needs to be reliable. Sikalastic-1K is the single-component answer for structures that move, containing water, or resisting aggressive environments. It’s the fibre-reinforced, crack-bridging cementitious mortar that ensures concrete stays protected and waterproofed, even under challenging conditions.

Why this product exists

Sikalastic-1K was developed to simplify flexible waterproofing and concrete protection. This one-component, fibre-reinforced, polymer-modified cementitious mortar delivers crack-bridging ability for various structures, including those designed to retain water. It stands as a reliable barrier against water ingress and environmental degradation, from basements facing negative water pressure to concrete tanks and under-tile wet areas.

The numbers that matter

Flexible waterproofing depends on the ability to handle movement. Sikalastic-1K provides a crack-bridging ability of greater than 0.50 mm (Class A3), or at least 0.75 mm under European standards (EN 14891). This means it maintains its integrity when minor substrate movement occurs, preventing water penetration through small cracks. Crucially for water-retaining structures, it demonstrates no water penetration after 72 hours at 5.0 bar of positive pressure and no penetration after 72 hours at 2.5 bar of negative pressure. This proves its capability to resist water from both sides, essential for basements and tanks. The product also boasts a strong tensile adhesion strength of at least 0.8 N/mm², even after exposure to water, heat, or freeze-thaw cycles. This ensures a durable bond to concrete, cement mortars, stone, and masonry, providing long-term protection.

What it's like to use

Sikalastic-1K arrives as a single component, requiring only the addition of water. Its consistency is adjustable for brush or trowel application, offering good sag resistance even on vertical surfaces. Before mixing, ensure substrates are structurally sound, clean, and free from contaminants. Concrete should be repaired using SikaTop or Sika MonoTop materials if required, then adequately dampened to a saturated surface dry (SSD) condition. Mix with a low-speed drill (around 500 rpm), ensuring a homogeneous, lump-free mortar. Apply in multiple thin layers; a total dry film thickness of 2 mm is standard, with 3-4 mm recommended for negative pressure or immersed applications. Maximum thickness per layer is 2 mm by trowel or 1 mm by brush, with subsequent layers applied crosswise after the previous one is dry. Tools clean easily with water before the material sets.

Where this product excels

• Water-retaining structures: Providing flexible waterproofing and protection for concrete tanks, basins, and pipes, ensuring integrity against water pressure.
• Under-tile wet areas: Serving as the primary waterproofing layer in bathrooms, showers, terraces, balconies, and swimming pools before the application of ceramic tiles, offering crack-bridging and adhesion properties.
• Basement waterproofing: Effective for internal waterproofing of walls and floors in basements, particularly against negative water pressure.
• Concrete protection: Acting as a flexible coating for reinforced concrete structures, protecting them from freeze-thaw cycles and carbon dioxide attack to enhance durability and extend service life.

How it fits in a real system

Sikalastic-1K typically forms the primary waterproofing layer within a system. After necessary substrate preparation and repairs with SikaTop or Sika MonoTop mortars, Sikalastic-1K is applied in multiple layers. For critical movement joints or junctions with vertical surfaces, reinforcement with Sika Seal Tape S is recommended, embedded directly into the fresh first layer and then covered by subsequent layers of Sikalastic-1K. For immersed and tanking applications, or where high movement is expected in joints, the Sikadur Combiflex SG System provides a dedicated solution. Once Sikalastic-1K has fully hardened (typically 2-7 days depending on temperature and exposure), ceramic or vitreous tiles can be installed using a polymer modified cement-based tile adhesive from the Sika range, ensuring all joints are sealed.

Choose this when

• When you need flexible, crack-bridging waterproofing: Its fibre-reinforced composition handles minor substrate movement, crucial for concrete structures.
• For one-component simplicity: Only water needs to be added, reducing mixing complexity on-site.
• To protect against negative water pressure: Proven resistance makes it suitable for internal basement waterproofing.
• As an under-tile waterproofing solution: Ideal for bathrooms, balconies, and swimming pools where tiles will be installed.
• For concrete protection against environmental factors: Shields reinforced concrete from freeze-thaw damage and carbonation.

Don't use this when

• Not for: Direct, unprotected contact with chlorinated water, such as in swimming pools, without suitable protective overcoating.
• Not for: High-movement expansion joints where the primary movement accommodation must come from the waterproofing layer itself, without integrating specific Sika joint systems like Sikadur Combiflex SG.
• Not for: Applications requiring a vapour barrier, as this product is permeable to water vapour.
• Not for: Smoothing with a float or trowel after application; its intended finish is functional, not decorative.
• Not for: Roof waterproofing where a liquid-applied membrane like Everflex WPM Under-Tile Waterproofing Membrane is a more appropriate and dedicated solution for external, exposed roofs.