Sikasil® WS-303 Weatherproofing sealant

Quick info

Weatherproofing sealant

Product Benefits
- Meets requirements of GB/T14683-2017,
- Outstanding UV and weathering resistance
- Adheres well to many substrates including glass, metals, coated and painted metals, plastics and wood

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Typical Product Data

Chemical base 1-C silicone
Cure mechanism Moisture-curing
Cure type Neutral
Density (uncured) (CQP 006-4) 1.4 kg/l
Non-sag properties (CQP 061-4 / ISO 7390) ≤ 2mm
Application temperature 5 - 40 °C
Skin time3(CQP 019-2) 30 min.
Elastic recovery(GB/T 14683/ISO 7389) 80%
Elongation at break (CQP 036-1 / ISO 37) 600 %
Tear propagation resistance (CQP 045-1 ) 4 N/mm
100% modulus (CQP 555-1 / GB/T 14683) 0.3 N/mm2
Thermal resistance (CQP 513-1)                                         4 hours

short term                                                                                  1 hour

200 °C

220 °C

Service temperature -40°C - 150 °C
Shelf life (storage below 25 °C) (CQP 016-1) 15 months

1) CQP = Corporate Quality Procedure 2) 23 °C (73 °F) / 50 % r.h.

Sikasil® WS-303 is a neutral-curing silicone sealant with a high movement capability and excellent adhesion to a wide range of substrates.

Product Benefits
- Meets requirements of GB/T14683-2017,
- Outstanding UV and weathering resistance
- Adheres well to many substrates including glass, metals, coated and painted metals, plastics and wood

Areas of Application
Sikasil® WS-303 can be used for weatherproofing and sealing applications where durability under severe conditions is required.
Sikasil® WS-303 is particularly suited as a weather seal for curtain walling and windows.
This product is suitable for professional experienced users only.
Tests with actual substrates and conditions have to be performed to ensure adhesion and material compatibility.

Cure Mechanism
Sikasil® WS-303 cures by reaction with atmospheric moisture. The reaction thus starts at the surface and proceeds to the core of the joint. The curing speed depends on the relative humidity and the temperature (see diagram 1). Heating above 50 °C to speed-up the vulcanization is not advisable as it may lead to bubble formation. At low temperatures the water content of the air is lower and the curing reaction proceeds more slowly.

Application Limits
Most Sikasil® WS, FS, SG, IG, WT,AS and other engineering silicone sealants manufactured by Sika are compatible with each other and with SikaGlaze® IG sealants. For specific information regarding compatibility between various Sikasil® and SikaGlaze® products contact the Technical Department of Sika Industry. All other sealants have to be approved by Sika before using them in combination with Sikasil® WS-303. Where two or more different reactive sealants are used, allow the first to cure completely before applying the next.
Do not use Sikasil® WS-303 on pre-stressed polyacrylate and polycarbonate elements as it may cause environmental stress cracking (crazing).
The compatibility of gaskets, backer rods and other accessory materials with Sikasil® WS303 must be tested in advance.
Joints deeper than 15 mm have to be avoided.
The above information is offered for general guidance only. Advice on specific applications will be given on request.

Method of Application
Surface preparation
Surfaces must be clean, dry and free from oil, grease and dust.Advice on specific applications and surface pretreatment methods is available from the Technical Department of Sika Industry.

After suitable joint and substrate preparation, Sikasil® WS-303 is gunned into place. Joints must be properly dimensioned as changes are no longer possible after construction. For optimum performance the joint width needs to be designed according to the movement capability of the sealant based on the actual expected movement. The minimum joint depth is 6 mm and a width / depth ratio of 2:1 must be respected. For backfilling it is recommended to use closed cell, sealant compatible foam backer rods e.g. high resilience polyethylene foam rod. If joints are too shallow for backing material to be employed, we recommend using a polyethylene tape. This acts as a release film (bond breaker), allowing the joint to move and the silicone to stretch freely.

For more information contact the Technical Department of Sika Industry.

Further Information
Copies of the following publications
are available on request:
- Safety Data Sheet
- General Guidelines: Solutions for Facades - Application of Sikasil® Weather Sealants

Packaging Information
Unipack 600 ml

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