- 1. Overview
- 2. Classification of formwork systems
- 3. Design parameters (IS 14687, IS 4990, IS 456)
- 4. Stripping time and reshoring
- 5. Surface finish grades (BS 8110 / IS 2571)
- 6. Accessories
- 7. Common failures and prevention
- 8. Testing and quality checks
- 9. Standards and references
- 10. Consultant checklist
- 11. Practical notes for site teams
- Disclaimer
Purpose: consultant-ready guide to formwork systems. Use the TOC to jump to system types, design parameters, stripping and reshoring, QA, defects, and standards.
1. Overview
Formwork is the temporary mold used to shape and support concrete until it gains sufficient strength to be self-supporting. Formwork quality controls surface finish, dimensional accuracy, cycle time, safety, and cost.
2. Classification of formwork systems
Category | Material | Key features | Common applications |
Timber formwork | Wood, battens | Easy to fabricate, economical for small works | Residential, short-term works |
Plywood formwork | Waterproof ply with timber backing | Smooth finish, lightweight | Beams, slabs, walls |
Steel formwork | Mild steel or GI plates | Durable, high strength, uniform finish | Heavy RCC, repetitive works |
Aluminum formwork (MIVAN) | Extruded aluminum panels | High precision, rapid cycle | High-rise, mass housing |
Plastic formwork | Modular interlocking panels | Lightweight, reusable | Low-rise, repetitive slabs |
Tunnel / system formwork | Integrated casting modules | Single pour for walls and slabs | Repetitive units, speed construction |
Jump / slip form | Mechanized moving system | Vertical progression | Cores, towers, silos, chimneys |
3. Design parameters (IS 14687, IS 4990, IS 456)
Parameter | Description | Acceptable range / criteria |
Form pressure | Fresh concrete lateral pressure | P = w × h (typical up to ≈ 50 kN/m² for vertical pours) |
Deflection limit | Deflection under load | ≤ span/270 (IS 456) |
Permissible stresses | Timber, steel, aluminum | Per IS 883, IS 800, IS 733 |
Surface finish tolerance | Dimensional deviations | ±6 mm alignment, ±3 mm flatness |
Contact surface | Finish requirement | F1 basic to F3 architectural |
Stripping time | Removal after strength gain | Per IS 456 Table 11 |
Reuse cycles | Expected repetitions | Steel 100–150, aluminum 200+, ply 8–12 |
4. Stripping time and reshoring
Member | Minimum stripping time (IS 456) | Concrete strength requirement |
Vertical sides (walls, columns) | 16–24 hours | Self-supporting |
Slab soffits (props left under) | 3 days | ≈ 70% design strength |
Beam soffits (props left under) | 7 days | ≈ 70% design strength |
Props under slabs (remove) | 7–10 days | Full design strength |
Props under beams (remove) | 14–21 days | Full design strength |
5. Surface finish grades (BS 8110 / IS 2571)
Finish type | Description | Typical usage |
F1 (basic) | Rough, for hidden surfaces | Foundations, below-ground |
F2 (standard) | Smooth, uniform | Slabs, beams, general concrete |
F3 (architectural) | High aesthetic quality | Exposed surfaces, facade concrete |
F4 (special) | Fine form-lined finishes | Architectural panels, special facades |
6. Accessories
Accessory | Function |
Tie rods and wing nuts | Resist lateral pressure |
Form oil / release agent | Prevent bonding to form |
Shuttering plywood | Smooth surface finish |
Props, soldiers, wales | Transfer vertical and lateral loads |
Spacer blocks / cover blocks | Maintain cover thickness |
Chamfer strips | Chamfered corners |
Jack props / adjustable spans | Support slabs and beams |
7. Common failures and prevention
Failure type | Root cause | Preventive measure |
Bulging or leakage | Poor joints, inadequate bracing | Tight joints, sufficient supports |
Honeycombing | Improper compaction, leaks | Proper vibration, seal joints |
Blowout (collapse) | Overpressure, poor ties | Design check, adequate ties and wales |
Surface discoloration | Uneven release agent | Uniform application, compatible products |
Alignment errors | Weak supports, settlement | Plumb and level checks before pour |
8. Testing and quality checks
Check | Frequency | Method |
Alignment and level | Each setup | Laser or theodolite |
Tightness and gaps | Before pour | Visual and light leak test |
Surface flatness | Post pour | 3 m straightedge |
Reuse cycle record | Every cast | Tagging and inspection |
Release agent uniformity | Each cycle | Test patch or visual check |
9. Standards and references
Code | Description |
IS 14687:2014 | Guidelines for formwork in concrete |
IS 4990:2011 | Plywood for concrete shuttering |
IS 5525:1969 | Scaffolding and shoring equipment |
IS 456:2000 | Concrete code including formwork removal |
IS 883:2016 | Timber design |
BS 8110 / EN 13670 | Execution and surface finish |
OSHA 1926.703 | Formwork safety and loads |
10. Consultant checklist
- Verify form pressure design for wall and column pours.
- Check material test certificates for steel and aluminum systems.
- Confirm tolerance and finish class before acceptance.
- Enforce reuse recordkeeping and panel condition checks.
- Confirm stripping and reshoring meet IS 456 requirements.
11. Practical notes for site teams
- Tighten ties and verify alignment before pouring.
- Apply uniform release agent; avoid diesel or kerosene.
- Pre-wet timber formwork to minimize absorption.
- Inspect gaps, joints, and plumb before concrete placement.
- Mark stripping dates on each panel.
Disclaimer
SpecX is a neutral, brand-agnostic resource based on standards and best practices. Cross-check with project requirements and local codes before finalizing specifications.