Sikalastic®-1K Mortar

For structural waterproofing of concrete, masonry, stone, and cement mortars, Sikalastic-1K Mortar provides a flexible, fiber-reinforced barrier that seals against both positive and negative water pressure. It is specified for tanks, basins, retaining walls, basements, and wet areas such as bathrooms, balconies, and swimming pools prior to tiling.

How it works

Sikalastic-1K Mortar is a single-component, polymer-modified cementitious system. Mixing the dry powder with water activates alkali-resistant polymers and integrated fibers, creating a highly workable slurry with excellent sag resistance on vertical surfaces. When applied, the mortar cures to form a crack-bridging membrane that accommodates thermal and structural movement without rupturing. Because it allows water vapour transmission, it permits damp substrates to breathe while stopping liquid water ingress, protecting reinforced concrete structures from the carbon dioxide and freeze-thaw exposure that drives reinforcement corrosion.

Numbers that matter

• 0.75 mm crack-bridging: Meets EN 14891 (at both +23 °C and -5 °C) to absorb substrate movement and prevent hairline cracks from telegraphing through finished tile installations.
• 2.5 bar negative pressure resistance: Prevents water penetration under negative hydrostatic pressure over 72 hours (UNI 8298/8), making it suitable for sealing the interior face of basement walls and floors.
• 5.0 bar positive pressure resistance: Withstands high head pressure over 72 hours (EN 12390-8 modified) to ensure long-term containment in deep tanks, basins, and swimming pools.
• ≥ 0.8 N/mm² tensile adhesion: Exceeds standard concrete bond requirements (EN 1542) to secure permanent adhesion to masonry, stone, and cementitious substrates.
• 30-minute pot life: Practical working window at +20 °C to mix, place, and finish the mortar before it begins to set.

Where to use it

• Immersed structures: Concrete tanks, basins, pipes, and swimming pools.
• Wet areas and balconies: Bathrooms, showers, terraces, and balconies before bonding ceramic tiles.
• Below-ground retaining walls: External concrete and masonry wall surfaces to be back-filled.
• Basements and cellar floors: Internal walls and floors subject to rising damp or negative hydrostatic water pressure.
• Concrete protection: Exposed reinforced concrete columns, beams, and facades vulnerable to carbonation and freeze-thaw cycles.

Application and system thickness

Prepare substrates by blast cleaning, high-pressure water-jetting (400 bar), grinding, or wire-brushing to remove laitance, coatings, grease, and dust. Repair any damage with SikaTop or Sika MonoTop mortars. Dampen the surface before application so it is moist but not saturated or wet to the touch.

Mix with a low-speed hand drill mixer (~500 r/min) for 3 to 4 minutes until lump-free. Adjust the consistency by changing the water ratio per 20 kg bag: use approximately 6.0 litres for brush application or 4.4 litres for trowel application.

• Standard applications: Apply at a minimum 2 mm dry film thickness (DFT) in at least two layers.
• Negative pressure and immersion: Apply at a total 3 mm to 4 mm DFT in at least two layers.
• Layer limits: Maximum thickness per layer is 2 mm when applied by trowel, and 1 mm when applied by brush. Apply subsequent coats crosswise once the preceding coat is dry.
• Joint detailing: Reinforce junctions, corners, and movement zones by bedding Sika Seal Tape S directly into the wet first layer, then overcoating with the second layer. Sika Seal Tape S is not suitable for swimming pools; use the Sikadur Combiflex SG System for immersed joints.

Limitations

• Do not smooth the fresh mortar surface using a sponge float or trowel. If a smooth finish is required, wait until fully cured and use light mechanical abrasion.
• Protect the freshly applied membrane from rain for at least 24 to 48 hours.
• Do not apply in direct sunlight, strong winds, or when rain is imminent.
• Avoid direct contact with chlorinated water in swimming pools; apply a suitable protective barrier or tiled finish over the cured mortar.
• When used for potable water storage, allow a 15-day cure at +20 °C before filling, then wash the surface thoroughly with water according to local regulations.
• Do not use as a vapour barrier for resin-based coatings that are impermeable to gas.
• Perform a preliminary compatibility patch test if applying solvent-based paints over the cured mortar to ensure solvents do not degrade the membrane.