Sikaflex®-428 Precast
1-PART FLEXIBLE SEALANT FOR CONCRETE PRECAST
Sikaflex®-428 Precast is a 1-component, moisture-curing, elastic joint sealant.
Suitable for use in hot and tropical climatic conditions.
- Good resistance to weathering
- Movement capability of ± 25 % (ASTM C 719)
- Over paintable
- Good adhesion to concrete
- Good application properties
- Low VOC content
Usage
Sikaflex®-428 Precast is designed for movement and connection joints between concrete precast elements,GRC and GRP parts. It is also suitable for masonry, concrete and block work joints, roof joints and terminations.
Advantages
- Good resistance to weathering
- Movement capability of ± 25 % (ASTM C 719)
- Over paintable
- Good adhesion to concrete
- Good application properties
- Low VOC content
Packaging
600 mL foil pack, 20 foil packs per box
Colour
White, off-white, concrete grey and beige (other colors on request)
Product Details
SUSTAINABILITY
Sikaflex®-428 Precast conforms to LEED® EQc 4.1
▪ VOC content < 45 g/l (US EPA Method 24)
APPROVALS / CERTIFICATES
- ASTM C 920 class 25
- BS EN 11600
Composition
Silane-Terminated Polyurethane
Shelf life
Sikaflex®-428 Precast has a shelf life of 12 months from the date of production, if it is stored in undamaged, original, sealed packaging, and if the storage conditions are met.
Storage conditions
Sikaflex®-428 Precast shall be stored in dry conditions, where it is protected from direct sunlight and at temperatures between +5 °C and +25 °C.
Density
| ~1.15 kg/l | (ISO 1183-1) |
Volatile organic compound (VOC) content
| < 45 g/l | (US EPA Method 24) |
Shore A Hardness
| ~28 (28d) | (ISO 868) |
Tensile Strength
| ~1.25 N/mm2 | (ASTM D-412-98a) |
Secant Tensile Modulus
| ~0.50 N/mm2 at 60 % elongation (23 °C) | (ISO 8339) |
Movement Capability
| ±25% | (ASTM C-719) |
Service Temperature
-40 °C min. / +80 °C max.
Joint Design
The joint width must be designed to suit the joint movement required and the movement capability of the sealant. The joint width shall be ≥ 10 mm and ≤ 50 mm. A width to depth ratio of 2 : 1 must be maintained (for exceptions, see table below).
Standard joint widths for joints between concrete element:
(Movement capability: ± 25 % (ASTM C719) and ΔT: 80 °C)
| Joint distance [m] | Min. joint width [mm] | Min. joint depth [mm] |
| 2 | 10 | 10 |
| 4 | 16 | 10 |
| 6 | 24 | 12 |
| 8 | 30 | 15 |
| 10 | 38 | 19 |
..
For larger joints following depth should be maintained:
| Joint width [mm] | Joint depth [mm] |
| 40 | 20 |
| 45 | 21 |
| 50 | 22 |
All joints must be correctly designed and dimensioned in accordance with the relevant standards, before their construction. The basis for calculation of the necessary joint widths are the type of structure and its dimensions, the technical values of the adjacent building materials and the joint sealing material, as well as the specific exposure of the building and the joints.
For more detailed advice and instructions please contact our Technical Department.
Application
Backing Material
Use closed cell, polyethylene foam backing rods or bond braker tapes.
Sag Flow
| no sag | (ASTM C-639-01) |
Ambient Air Temperature
+5 °C min. / +45 °C max. (min. 3 °C above dew point temperature)
Substrate Temperature
+5 °C min. / +45 °C max.
Curing Rate
| ~4 mm/24 h (23 °C / 50 % r.h.) | (CQP 049-2) |
Skinning time
| ~50 min (23 °C / 50 % r.h.) | (CQP 019-1) |
Consumption
| Joint length [m] per 600 ml foil pack | Joint width [mm] | Joint depth [mm] |
| 6 | 10 | 10 |
| 4 | 15 | 10 |
| 3 | 20 | 10 |
| 2 | 25 | 12 |
| 1.3 | 30 | 15 |
| 0.8 | 45 | 20 |
| 0.5 | 50 | 22 |
SUBSTRATE PREPARATION
Sikaflex®-428 Precast generally has strong adhesion without primers or activators to most clean, dry and sound precast concrete substrates.
The substrate must be clean, dry, sound and homogeneous, free from oils, grease, dust and loose or friable particles. Sikaflex®-428 Precast adheres without primers and/or activators.
However, for optimum adhesion and critical, high performance applications, such as on multi-story buildings, highly stressed joints, and/or extreme weather exposure, the following priming and/or pre-treatment procedures shall be followed:
Porous substrates
Concrete, aerated concrete and cement based renders, mortars and bricks shall be primed using Sika® Primer-3 N applied with a brush. Before sealing, allow a flash-off time of > 30 minutes (< 4 hours).
For more detailed advice and instructions please contact our Technical Department.
Note: Primers are adhesion promoters. They are neither a substitute for the correct cleaning of a surface, nor do they improve the strength of the surface significantly.
CLEANING OF EQUIPMENT
Clean all tools and application equipment immediately after use with Sika® Remover-208 and/or Sika® Top-Clean T. Once cured, residual material can only be removed mechanically.