Curing and Striking Time: What It Means for Tie Hardware
> In brief > - The strength available at striking is what the tie rod has to work with. > - Early striking moves load onto the hardware interface. > - The striking sequence is a technical decision, not a calendar date.
Striking time is usually discussed as a concrete issue, but it is also a hardware issue: releasing ties too early damages the concrete around the cone, and releasing them carelessly damages the hardware and shortens its reuse life.
Our own production and test data are available on request — see how our factory works and contact the engineering team for the documents behind any figure quoted here.
Striking time is the period after which formwork can be removed based on the concrete's achieved strength. Cone refers to the component that sits in a recess formed in the concrete face during the curing process. Tie rods are the fasteners used to secure formwork panels, which should be released last to prevent damage. Maturity means the development of concrete strength over time, influenced by temperature and mix design.
Strength at striking.
Formwork is normally struck when the concrete has reached a specified proportion of its design strength — commonly 30-50% for vertical formwork — a working range rather than a fixed code figure, since ACI 347 leaves the striking decision to the structural engineer, with higher values where the surface will be loaded or where the wall is tall. The controlling factor is the least mature part of the pour, which is the top, not the base.
In cold weather, maturity develops far more slowly. A wall that is ready at 24 hours in summer may need 48-72 hours at 5 °C. Striking to a timetable rather than to a measured or calculated maturity is the usual cause of edge damage and, occasionally, of a wall that deflects when the formwork is removed.
Standard basis: EN 13670 — Execution of concrete structures
What early striking does to the hardware interface.
The cone sits in a recess formed in the concrete face. If the concrete has not gained enough strength, the cone is extracted by tearing the concrete rather than sliding out, which leaves a jagged, oversized recess that then needs more mortar and provides less durable cover.
The same applies to embedded anchors: withdrawing or loading them too early can pull a cone of concrete with them, compromising the anchor for its permanent role if it is a permanent type.
Standard basis: ACI 347 — Guide to formwork for concrete
Striking sequence.
Release the tie rods last, after the panel has been separated from the face and is supported. Releasing ties first lets the panel drop onto the tie holes, damaging both the panel and the concrete edge at the tie positions.
Work from the top down on tall walls, keeping the lower ties engaged until the upper panels are clear. This keeps the panel from swinging and preserves the lower tie positions.
For climbing systems, follow the sequence defined by the system: the climbing unit is transferred only after the anchor in the new lift has reached its transfer strength.
Maintenance after striking.
Clean and inspect the rods immediately. Concrete residue on threads is abrasive, and a rod that is stacked with residue on the thread will be damaged in handling before the next cycle.
Re-oil the unthreaded shank and the thread lightly. Release agent belongs on the formwork face and on the cone body, not in the thread.
Segregate damaged rods rather than returning them to general stock. A rod that will not accept a nut by hand is a rejected part; mixing it into a bundle moves the problem to the next pour.
What to record.
Keep the pour date, the concrete temperature and the striking date for each lift. When a wall shows edge spalling, the record shows whether it was a striking issue, a mix issue or a handling issue — and that determines who fixes it.
| Striking Time | Concrete Strength Proportion | Consequences for Hardware and Concrete |
|---|---|---|
| 30-50% | Vertical formwork standard | Minimizes edge damage, preserves hardware |
| 48-72 hours | 5 degC cold weather condition | Prevents premature extraction, reduces spalling |
| 24 hours | Summer condition | Risk of edge damage, compromised anchors |
| Top-down sequence | Tall wall striking | Prevents panel swinging, protects lower tie positions |
| Last to release | Tie rods in sequence | Avoids panel drop, minimizes concrete edge damage |
References and standards.
- EN 13670 — Execution of concrete structures
- ACI 347 — Guide to formwork for concrete
- OSHA 1926.703 — Concrete equipment and formwork
- OSHA concrete safety and health topics
- EN 10204:2004 — Types of inspection documents
- ISO 898-1 — Mechanical properties of fasteners made of carbon steel
About us: This article covers the relationship between curing, striking time, and tie hardware. Our production and test data are available on request. Our contact page provides a way to reach our engineering team for detailed information, and the about page documents our factory processes. This article was reviewed by the Qianheng Formwork Engineering team.