Sikasil WS-290

Ultra low modulus, neutral cure silicone sealant

Sikasil WS-290 is a one-part, neutral-curing, ultra low-modulus, low to no bleed silicone sealant that cures to a durable, flexible building sealant Sikasil WS-290 performs exceptionally well under dynamic conditions due to its ultra-low modulus, high extension/compression, recovery properties and strong adhesion to most building materials. Sikasil WS-290 accommodates long-term movement of +100-50% in properly designed joints and is particularly well suited for use in Exterior Insulation Finish Systems (EIFS). Meets the requirements of ASTM C-920, Type S, Grade NS, Class 100/50, Use NT, M, G, A, O; TT-S-00230C, Type II, Class A; TT-S-001543A, Class A; CAN/CGSB-1 9.1 3-M87, AAMA 808.3

Where To Use

  • Sealing expansion and control joints in precast concrete panels and metal curtain walls
  • As a weatherseal in glass to glass butt joint glazing
  • As a weatherseal in both conventional glazing and structural glazing* applications, including cap, toe and heel beads
  • Exterior Insulation Finish Systems (EIFS) and numerous other areas requiring a high-performance sealant


  • Unaffected by most atmospheric conditions
  • Non-staining
  • Joint movement +100/-50%
  • Excellent adhesion
  • One-component
  • Excellent gunnability in all temperatures
  • Ultra low Modulus

How to use:


The number of joints and the joint width should be designed for a maximum of +100 and -50% movement of joint width at time of installation. The depth of the sealant should be 1/2 the width of the joint. The maximum depth is 1/2 inch (13mm) and the minimum is 1/4 inch (6mm). To control joint depth, use closed cell polyethylene, non-gassing polyolefin or open cell polyurethane backer rod. If joint depth does not allow for backer rod, use polyethylene bond breaker tape to prevent three-sided adhesion. Closed cell backer rod should be 25% larger than joint width; do not compress more than 40%. Open cell should be compressed 40%. Do not use open cell rod in horizontal on grade joint or with E.I.F.S. When installing during time of large temperature swings such as spring or fall, and in joints designed for movement greater than ± 25 %, be aware of the significant joint movement before cure, may cause aesthetic issues such as ripples in the sealant surface. Performance will not be affected. Ready to use, apply using professional caulking gun. Do not open product container until preparation work has been completed. Apply sealant using consistent, positive pressure to force sealant into the joint. Tool sealant to create a concave joint shape and maximum adhesion. Dry tooling is recommended. DO NOT use soapy water or other liquids when tooling.


See data sheet.