How Long Before Removing Forms from Concrete in Construction?

One of the most important stages in concrete construction is form removal, also known as form stripping. Forms provide the temporary mold that holds wet concrete in place until it hardens and gains strength. But how long should you wait before removing those forms?

The answer depends on the type of concrete, the structure being poured, weather conditions, and strength development. Removing forms too early can weaken the structure, while waiting too long may slow down the project and increase labor costs.

In this article, we’ll explain exactly how long you should wait before removing concrete forms, based on industry guidelines, structure type, and field conditions.

What Are Concrete Forms?

Concrete forms are temporary molds or structures made of wood, steel, aluminum, or plastic that hold wet concrete in place while it cures. Once the concrete sets and achieves sufficient strength, these forms are removed.

They’re used for:

• Foundations
• Columns and beams
• Walls
• Slabs
• Stairs
• Footings

General Rule: Wait for Concrete to Gain Strength

Concrete should not be stripped from its forms until it gains enough strength to support its own weight and any imposed loads.

Standard concrete reaches 70% of its design strength within 7 days.

However, the timing for form removal is not fixed and must be based on real-world conditions and professional guidelines.

Typical Timeframes for Removing Concrete Forms

These timeframes are based on standard curing conditions (about 20°C or 68°F) with ordinary Portland cement.

Factors Affecting Form Removal Time

Several factors impact how fast concrete cures and how soon forms can be removed:

1. Concrete Mix Type

• High early-strength concrete allows faster form removal.
• Mixes with retarders slow down the curing process.

2. Weather and Temperature

• Cold weather slows down strength gain.
• Hot weather speeds up curing but can cause surface cracking if not cured properly.

3. Form Material

• Metal forms can be removed earlier as they conduct heat and speed up setting.
• Wood forms may need more time due to slower hydration.

4. Load Conditions

• If the element is load-bearing, wait until concrete reaches at least 70% of its design strength.
• Non-load-bearing forms (like vertical sides of walls) can be removed earlier.

5. Curing Conditions

• Proper curing (moisture, temperature, and time) ensures safe and timely form removal.

What Strength Should Concrete Reach Before Removing Forms?

Field engineers often use concrete cylinder tests to measure compressive strength before stripping forms.

Best Practices for Form Removal

To ensure safety and quality, follow these best practices when removing forms from concrete:

✅ Follow the Engineer’s Instructions

Always defer to the structural engineer’s specific schedule.

✅ Start with Non-Load-Bearing Forms

Side forms (like those on walls and columns) can often be removed earlier than bottom supports.

✅ Be Gentle

Use pry bars, wedges, and light tapping to avoid chipping or cracking the concrete.

✅ Keep Curing

Even after forms are removed, concrete needs continuous curing for up to 28 days for full strength development.

✅ Inspect Edges and Corners

Concrete is weakest at corners. Check for strength before removing formwork from these areas.

Form Removal Time Under Different Conditions

Importance of Proper Timing

Removing forms too early can cause:

• Cracking
• Sagging of slabs
• Structural failure
• Rework and costly delays

Leaving forms too long may result in:

• Increased labor costs
• Surface discoloration or bonding issues
• Difficulty in removal, especially for wood forms

Code and Standard References

🔸 ACI 347R-14 – Guide to Formwork for Concrete

Specifies recommended form removal times based on element type and strength.

🔸 OSHA Construction Guidelines

Ensures safe working conditions during stripping operations.

🔸 ASTM C31

Outlines procedures for preparing and curing test cylinders used to determine in-place concrete strength.

Table: Summary of Recommended Form Removal Times

Concrete Strength Testing Options

If you’re unsure whether the concrete has gained enough strength, these methods help:

✅ Cylinder Compression Testing

Field-cured cylinders are crushed at a lab to measure compressive strength.

✅ Maturity Method

Measures time-temperature history of concrete using sensors embedded during placement.

✅ Rebound Hammer Test (Schmidt Hammer)

Non-destructive test used to estimate surface hardness and strength.

Conclusion

The timing for removing concrete forms is not a one-size-fits-all answer. It depends on several key variables including the type of structure, mix design, weather conditions, and strength development.

General timelines range from 24 hours for walls to 14 days for beams and slabs, but field testing and professional guidelines should always be followed. Correct form removal ensures safety, quality, and project efficiency.

Whether you’re a contractor, builder, or project manager, understanding the science behind form stripping can prevent costly mistakes and ensure a structurally sound result.

FAQs: How Long Before Removing Forms from Concrete in Construction?

1. Can I remove concrete forms after 24 hours?

Yes, for vertical elements like walls and columns, side forms can often be removed after 24–48 hours if curing conditions are favorable.

2. How long should I leave slab formwork in place?

Slabs generally require at least 7 days before removing bottom forms. Edge forms may be removed after 3–4 days.

3. Can forms be removed earlier in hot weather?

Possibly, since heat accelerates curing. However, be careful of surface cracking. Always confirm strength before stripping.

4. Is form removal time the same for all concrete types?

No. High early-strength concrete cures faster. Mix design greatly affects stripping time.

5. What happens if I remove the forms too soon?

Early removal can result in cracks, sagging, or even failure of the concrete structure.

6. What is the minimum strength required to strip forms?

Generally, 500–700 psi for vertical forms and 70% of design strength for slabs and beams.

7. Do I need to continue curing after removing forms?

Yes. Continue curing using water spray, wet burlap, or curing compound for at least 7 days.

8. Who decides when to remove forms on a job site?

Typically, a site engineer or project manager, often based on lab test results or construction codes.

9. Is it safe to walk on concrete right after form removal?

Only if the concrete has reached adequate load-bearing strength, generally at least 70% of its design value.

10. Can I reuse the same forms on the next pour?

Yes, especially for metal or plastic forms. Clean and inspect them before reuse. Wood forms can also be reused a few times if undamaged.