Design Width
6–10 mm
Function
Controls shrinkage cracks
Material
PU sealant
Movement
Small (tensile)
Typical Application Detail
Industrial floors / pavements
Typical Locations
Industrial floors, pavements
Waterproofing Approach
Saw-cut + sealant
1. Introduction
Contraction joints are deliberate cracks introduced in large slabs or floors to control shrinkage stresses and prevent random cracking.
They are typically shallow, saw-cut grooves filled with flexible sealant.
2. Common Failures
- Delay in saw-cutting causing random cracks.
- Sealant not installed or rigidly filled.
- Dirt or moisture in joint groove before sealing.
3. System Requirements
- Early-age cutting (within 12–24 hrs after casting).
- Flexible filler to absorb shrinkage stresses.
- Watertight, dust-free joint surface.
4. Recommended Systems
Application | Material | Notes |
Internal floors | PU or polysulphide sealant | Semi-rigid preferred for traffic |
External slabs | PU sealant + backer rod | UV stable, flexible system |
5. Methodology
- Saw-cut groove to ¼ slab thickness.
- Clean and vacuum out dust.
- Insert backer rod and apply primer.
- Apply sealant neatly with slight concave profile.
6. Performance Parameters
Property | Requirement | Standard |
Movement capability | ±25% | ASTM C719 |
Shore A hardness | 35–50 | ASTM D2240 |
Adhesion | ≥1.0 N/mm | ASTM C794 |
7. QA/QC Checklist
- ☑ Saw-cut within 24 hrs
- ☑ Dust removed prior to sealing
- ☑ Correct backer rod size
- ☑ Sealant cured properly
Video Masterclass
SpecX Masterclass: Contraction/ Induced Joint Solutions → Coming Soon
Disclaimer
SpecX is an industry initiative & a neutral resource, compiled from industry references and best practices. It is not brand-specific. Always cross-check with project requirements and local codes before finalizing specifications.