One-component adhesive and sealant

Sikaflex®-221i is a high-quality, multifunctional, stable, one-component polyurethane adhesive and sealant. The product cures by exposure to air humidity. Sikaflex®-221i is used for general waterproofing and for applications in lightweight construction.


1 Component formulation




Low odour


Product advantages

  • 1 component formulation
  • Elastic
  • Low odour
  • Non-corrosive
  • Recoatable
  • Sandable
  • Wide adhesion spectrum
  • Solvent-free and very low VOC
  • Low isocyanate content


Sikaflex®-221i adheres well to a variety of substrates and is suitable for elastic, permanent waterproofing. Suitable substrates are metals, primers and paints (two-component systems), ceramic materials and plastics. Observe manufacturer’s recommendations before using Sikaflex®-221i on materials at risk of stress cracking. Pre-tests must be carried out with original materials to avoid stress cracking. This product is only suitable for experienced users. To ensure adhesion and material compatibility, preliminary tests must be carried out with original materials under the relevant conditions.

Product details

Product features

Chemical base 1-component polyurethane
Colour (CQP001-1) White, grey, black
Curing mechanism Moisture-curing
Density before curing Depending on colour 1.3 kg/l
Stability Good
Application temperature Environment 10 to 40 °C
Skin formation time (CQP019-1) 60 minutes
Through-curing speed (CQP049-1) See diagram 1
Volume change (CQP014-1) -3 %
Hardness Shore A (CQP023-1 / ISO 7619-1) 45
Tensile strength (CQP036-1 / ISO 527) 1.8 MPa
Elongation at break (CQP036-1 / ISO 527) 700 %
Tear resistance (CQP045-1 / ISO 34) 8 N/mm
Operating temperature (CQP513-1) -50 to 90 °C
4 Hours 120 °C
1 Hour 140 °C
Durability (CQP016-1) Cartridge / Bag 12 Months

Technical information

Sikaflex®-221i cures by reaction with air humidity. At low temperature the water content of the air is lower and the cross-linking reaction is somewhat slower, see diagram 1.

Sikaflex®-221i is generally resistant to fresh water, sea water, dilute acids and dilute alkalis; temporarily resistant to fuels, mineral oils, vegetable and animal fats and oils; not resistant to organic acids, glycol, concentrated mineral acids and alkalis or solvents.


Surface pretreatment

The adhesive surfaces must be clean, dry and free from grease, oil and dust.

The surface pre-treatment depends on the specific nature of the substrate and is decisive for a durable bond. Information on substrate pretreatment can be found in the current Sika® pretreatment table. The information contained there is based on experience and must always be verified by preliminary tests with original materials.


The optimum temperature for substrate and sealant is between 15 °C and 25 °C.

Apply Sikaflex®-221i with a suitable cartridge/bag gun or pumping equipment. For information on the selection and installation of a suitable pump system, please contact the System Engineering Department at Sika Industry.


Smoothing must be carried out before the sealant skin forms. For smoothing we recommend Sika® smoothing agent N. Other smoothing agents must be checked for their suitability.


Sikaflex®-221i can be painted over after skin formation. The adhesion of the coating can be improved by pre-treating the joint surface with Sika® Aktivator-100 or Sika® Aktivator-205 before coating. If the paint requires a baking process, the best result is obtained when the sealant has fully cured beforehand. Paint compatibility must be checked by preliminary tests under production conditions. As the elasticity of the paint is lower than that of the sealant, paint cracks may occur in the joint area.