Form Determination to Remove Forms and Shores Is Based On in Construction

In concrete construction, formwork and shoring systems are vital for supporting fresh concrete until it reaches the required strength to support its own weight and any imposed loads. But one of the most crucial—and frequently misunderstood—decisions in this process is determining when to remove forms and shores.

Improper timing can lead to structural damage, project delays, and safety hazards. Therefore, understanding what the form determination to remove forms and shores is based on is essential for engineers, contractors, and site supervisors alike.

This in-depth guide explores all the factors that govern safe and effective removal of formwork and shoring in construction.

What Are Forms and Shores in Concrete Construction?

• Forms (formwork): Temporary molds—usually made of wood, steel, aluminum, or plastic—that give concrete its shape while it’s still wet.
• Shores (shoring): Temporary vertical supports used to carry the weight of freshly placed concrete until it gains sufficient strength, especially for slabs and beams.

Both systems are temporary but essential, and their timely removal ensures structural safety and construction efficiency.

Why Proper Timing Matters

Removing forms and shores too soon can result in:

• Cracking
• Deflection
• Structural failure
• Surface spalling
• Costly repairs or reconstruction
• Delays and safety violations

Delaying removal unnecessarily, on the other hand, ties up materials, labor, and limits progress on subsequent construction tasks.

What Is Form Determination Based On?

The decision to remove forms and shores in construction is based on multiple factors, with concrete strength being the most critical.

✅ 1. Concrete Compressive Strength

This is the primary determinant for safe removal.

• The concrete must achieve a minimum percentage of its design compressive strength before removing forms or shoring.
• For slabs and beams, typically 70–100% of the design strength is required.
• For vertical elements like walls and columns, early removal is possible at lower strength levels (~500–700 psi), provided they are not under load.

✅ 2. Structural Function and Load Conditions

• Elements that support other components (e.g., slabs, beams) need to retain shores longer than elements that don’t carry additional loads.
• For multi-story structures, reshoring may be needed after formwork removal.

✅ 3. Type of Concrete Mix

• High-early-strength concrete allows earlier removal.
• Pozzolanic and retarded mixes cure more slowly and require longer form retention.

✅ 4. Environmental Conditions

✅ 5. Curing Methods

• Adequate curing improves early strength development.
• Poor or inconsistent curing delays form removal and weakens the structure.

✅ 6. Concrete Member Size and Shape

• Larger elements take longer to set due to heat retention and slower hydration in the core.
• Thin elements cure faster and can often be stripped sooner.

Strength Benchmarks for Form and Shore Removal

These are estimates under standard conditions (~20°C / 68°F). Always verify with testing and site-specific factors.

Approved Methods to Confirm Form Removal Readiness

🧪 Cylinder Compression Tests (ASTM C39)

• Most common method
• Tests strength of sample concrete cylinders

🛠️ Rebound Hammer Test (ASTM C805)

• Non-destructive surface hardness test
• Gives approximate indication of strength

📈 Concrete Maturity Method (ASTM C1074)

• Uses time-temperature data
• Calculates strength development based on curing history

📋 Engineer’s Inspection & Approval

• Structural engineer may require formal inspection and test data
• Especially for critical load-bearing components

Sequence of Form and Shore Removal

1. Side forms of vertical elements
   Removed first (e.g., walls, columns) after achieving minimum surface strength.
2. Soffits and bottom forms
   Must be retained until full strength is reached.
3. Props and shores
   In slabs and beams, shores may remain after form removal and should only be taken out when full design strength is confirmed.
4. Reshoring (if needed)
   In multi-story construction, reshoring helps support the structure during load transfer.

Industry Standards and Guidelines

These documents are essential references for ensuring safe, legal, and effective form and shore removal.

Best Practices for Safe Form and Shore Removal

• Plan in advance: Assign responsibilities for removal schedules and testing.
• Mark formwork with pour and removal dates.
• Continue curing even after form removal to promote long-term strength.
• Remove forms gently using the right tools—avoid prying or hammering that may damage edges.
• Monitor ambient conditions and adjust timelines as needed.
• Communicate with your team: Engineers, site supervisors, and labor must be aligned on timing and methods.

Common Mistakes to Avoid

Quick Reference Table: When to Remove Forms and Shores

Conclusion

In construction, the determination to remove forms and shores is based on a careful evaluation of concrete strength, environmental conditions, structural requirements, and industry standards. It’s not simply about waiting a few days—it’s about ensuring the concrete is strong enough to support itself and any loads it may bear.

Failing to base form and shore removal on strength verification and engineered guidance can result in serious structural problems, safety violations, and costly setbacks. Always rely on testing, inspection, and code compliance to ensure the job is done safely and correctly.

FAQs: Form Determination to Remove Forms and Shores Is Based On

1. What is the main factor in deciding when to remove concrete forms?

The most important factor is concrete compressive strength, not just the number of days passed since pouring.

2. Can I remove shores once forms are off?

Not necessarily. Shores support structural loads and must stay in place until full design strength is achieved.

3. How do I know if concrete has reached the required strength?

By conducting field or lab tests like compression testing, rebound hammer testing, or using the concrete maturity method.

4. Can forms be removed earlier in hot weather?

Yes, warmer temperatures accelerate curing, but strength tests should still confirm adequate hardness before removal.

5. Are there industry standards for shore removal?

Yes. ACI 347R, ACI 301, and OSHA Subpart Q all provide guidelines for safe form and shore removal.

6. What’s the risk of removing forms too early?

Risks include cracks, deflection, collapse, or permanent structural damage.

7. Is reshoring required after removing shores?

In multi-story structures, reshoring helps distribute loads and is often required until all levels gain sufficient strength.

8. Can I just follow a time-based schedule?

No. Always verify strength before removing critical supports. Time is a guideline—not a guarantee.

9. Does form material affect removal time?

Yes. Steel and aluminum forms cool faster, sometimes allowing earlier removal than wood forms, which retain moisture.

10. Who makes the final call on removing forms and shores?

Usually the site engineer or project manager, based on test data, project specifications, and safety standards.