Shuttering Magnets for Precast Concrete: Selection, Use and Maintenance

Shuttering magnets are widely used to secure side forms, block-outs and other formwork components to steel casting tables. Compared with drilling, welding or permanently fixing the formwork, a magnetic shuttering system allows the production layout to be changed more quickly between precast concrete elements.

The principle is straightforward: place the shuttering magnet on the steel table, press the activation button and connect it to the formwork profile. In practice, reliable performance depends on the magnet’s holding force, the condition of the casting table, the formwork height, the concrete pressure and correct daily maintenance.

An oversized magnet may increase cost and make handling more difficult. An undersized magnet can allow the formwork to move during concrete placement or vibration.

This guide from WZ Magnetics Co., Ltd. explains how to select and use shuttering magnets in precast concrete production.

What Is a Shuttering Magnet?

A shuttering magnet is a switchable magnetic assembly designed to hold precast concrete formwork on a ferromagnetic casting table.

It normally contains:

• High-performance permanent magnets
• A steel magnetic circuit
• An activation button
• A spring or switching mechanism
• A protective steel housing
• Connection points for adapters or formwork profiles

When the unit is activated, the internal magnetic circuit directs magnetic flux into the steel table. This produces the holding force needed to keep the formwork in position.

To release the magnet, an operator uses a suitable lifting or release tool. The mechanism separates the active magnetic section from the casting table and returns the unit to its released position.

The magnet does not turn permanent magnetism on and off electrically. The operating mechanism changes the magnetic circuit and the position of the magnetic assembly relative to the steel surface.

Why Are Shuttering Magnets Used?

Traditional formwork installation may involve welding stops, drilling holes or attaching fixed mechanical components to the casting table. These methods can take time and may damage the table surface.

A magnetic shuttering system offers several practical advantages:

• Faster positioning of side forms
• Easier changes between different panel sizes
• Reduced need for welding
• Less damage to casting tables
• Reusable mounting components
• Cleaner working areas
• More flexible production layouts
• Reduced setup time between products

These advantages are most valuable in plants that manufacture different precast concrete components on the same casting line.

Shuttering magnets are commonly used for:

• Wall panels
• Floor slabs
• Beams
• Columns
• Stairs
• Balconies
• Double-wall elements
• Sandwich panels
• Utility products
• Customized precast components

The required system depends on the dimensions and production method of the concrete element.

How Does a Shuttering Magnet Work?

When activated on a steel casting table, the shuttering magnet forms a closed magnetic circuit through the contact surface. This creates a strong downward attraction.

The magnet itself usually provides vertical holding force against the steel table. Adapters, brackets or integrated profiles transfer the horizontal pressure from the concrete into the magnetic unit.

Reliable holding depends on:

• Magnet design
• Contact area
• Casting table thickness
• Table flatness
• Surface cleanliness
• Formwork geometry
• Concrete pressure
• Vibration
• Position of the applied load

The rated force is usually measured under controlled vertical pull-off conditions. Actual formwork loading may include horizontal pressure, vibration and leverage, so the quoted value should not be treated as the complete structural capacity of the formwork system.

Main Components of a Magnetic Shuttering System

A complete magnetic shuttering system includes more than the magnet box.

Shuttering Magnet

The magnet provides the clamping force against the steel casting table.

Formwork Profile

The profile creates the edge shape of the precast concrete component. It may be made from steel, aluminum, wood or another suitable material.

Adapter

An adapter connects the magnet to the formwork profile and transfers forces between them.

Release Tool

The release tool lifts the activation button or operating mechanism. It allows operators to deactivate the magnet without striking or prying directly against the housing.

Casting Table

The steel casting table completes the magnetic circuit and provides the base for the formwork system.

Each component must work together. A high-capacity shuttering magnet cannot compensate for a weak adapter, deformed formwork or unsuitable casting table.

How Much Holding Force Is Required?

Shuttering magnets are available in different force classes. The required capacity depends on the concrete element and production conditions.

Important factors include:

• Formwork height
• Formwork length
• Fresh concrete pressure
• Pouring speed
• Concrete consistency
• Vibration method
• Distance between magnets
• Adapter geometry
• Casting table condition
• Required dimensional accuracy

A low side form for a thin slab does not experience the same loading as a tall wall-panel form.

Instead of selecting the magnet by formwork height alone, assess the force acting on each section of the system.

Fresh Concrete Pressure

Fresh concrete applies lateral pressure to the formwork. This pressure generally increases with depth, which means the lower part of a tall form can experience greater pressure than the upper part.

Actual pressure depends on:

• Concrete density
• Pouring height
• Pouring speed
• Concrete workability
• Setting behavior
• Temperature
• Vibration
• Formwork shape

Vibration can temporarily increase the load and may cause poorly secured forms to move. The magnet spacing and adapter design should therefore be reviewed for the complete casting process.

For tall or heavily loaded forms, magnetic holding may need to be combined with additional bracing.

Rated Pull Force vs Working Capacity

A shuttering magnet may be advertised as 600 kg, 900 kg, 1,350 kg or another nominal force. This normally refers to a vertical pull-off test conducted on a defined steel plate.

It does not mean the unit can resist the same value in every direction or under every condition.

Real performance can be reduced by:

• Concrete residue
• Rust
• Paint
• Thin steel
• Uneven casting tables
• Partial contact
• Damaged magnet faces
• Incorrect activation
• Side loading
• Vibration

The quoted holding force should be used for model comparison and preliminary system design. The actual arrangement should be verified during trial production.

Common Shuttering Magnet Force Classes

The following table provides a general starting point rather than a final engineering rule:

The correct model depends on concrete pressure, magnet spacing and adapter design. Two projects using formwork of the same height may still require different magnetic arrangements.

Determine the Magnet Spacing

Magnet spacing affects both formwork stability and total system cost.

If magnets are placed too far apart:

• Formwork may bend between mounting points.
• Joints may open.
• Concrete may leak.
• Panel dimensions may move out of tolerance.
• Vibration may shift the form.

If magnets are placed unnecessarily close together:

• Setup takes longer.
• More units must be purchased and maintained.
• Operators handle more equipment.
• Cleaning requirements increase.

Spacing should be determined by the formwork stiffness and expected load per unit length.

A trial casting is useful for checking:

• Formwork deflection
• Joint movement
• Concrete leakage
• Magnet displacement
• Dimensional accuracy

The final spacing can then be standardized for recurring products.

Check the Casting Table

The casting table is part of the magnetic circuit and has a direct effect on shuttering magnet performance.

Steel Thickness

If the steel plate is too thin, it may not carry the full magnetic flux. Holding force can be lower than the value measured on a thicker factory test plate.

Flatness

Warped or damaged tables prevent full contact between the magnet and steel.

Even a small local gap can reduce holding force.

Surface Condition

Concrete residue, welding spatter, paint, rust and dirt create non-magnetic gaps.

The contact area should be cleaned before the magnet is positioned.

Table Structure

The support structure under the steel plate can affect stiffness and local deflection. A flexible table may move under loading and create uneven contact.

Before purchasing shuttering magnets, provide the steel table material, plate thickness and surface condition to WZ Magnetics Co., Ltd.

Select the Right Formwork Adapter

The adapter transfers forces between the formwork and the shuttering magnet. Its geometry is as important as the magnet’s rated force.

Adapters may be designed for:

• Steel side forms
• Aluminum profiles
• Wooden formwork
• Integrated magnetic profiles
• Block-outs
• Window and door openings
• Customized edge shapes

A suitable adapter should:

• Fit the formwork profile accurately
• Resist bending
• Keep the form stable
• Be easy to install and remove
• Avoid interfering with concrete placement
• Allow access to the magnet release button
• Transfer the load without creating excessive leverage

Poorly designed adapters may place the load too far from the magnet. This creates a turning moment and increases the risk of movement or peeling.

Standard Magnet Box or Integrated Magnetic Formwork?

There are two common approaches.

Separate Magnet Boxes

A separate magnet box is positioned beside the formwork and connected through an adapter.

Advantages include:

• Flexible placement
• Easy replacement
• Compatibility with multiple profiles
• Convenient maintenance
• Lower cost for varied production

This approach is well suited to factories producing different components.

Integrated Magnetic Formwork

In an integrated system, magnets are built into the formwork profile.

Advantages may include:

• Faster setup
• Fewer loose components
• Consistent magnet spacing
• Easier handling for repeated products
• More standardized production

Integrated systems usually require more customized design and may be less flexible when product dimensions change frequently.

How to Install a Shuttering Magnet

A typical installation process includes the following steps.

1. Clean the Contact Surfaces

Remove concrete residue, rust, dust and other debris from both the casting table and magnet face.

2. Position the Formwork

Place and align the side form according to the production drawing.

3. Position the Shuttering Magnet

Set the magnet in the correct location without activating it too early. Keep hands away from the bottom contact area.

4. Connect the Adapter

Ensure the adapter sits correctly against the formwork and magnet housing.

5. Activate the Magnet

Press the operating button using the approved method. Confirm that the magnet is fully engaged.

6. Check Alignment

Inspect formwork dimensions, joints and magnet spacing before pouring concrete.

7. Monitor During Casting

Observe the formwork during pouring and vibration. Stop the process if movement, leakage or abnormal deflection occurs.

Installation procedures should follow the factory’s safety rules and the operating instructions supplied with the magnetic system.

How to Release a Shuttering Magnet

After the concrete has reached the required condition for demolding:

1. Remove any load from the adapter.
2. Clear concrete residue around the magnet.
3. Position the correct release tool.
4. Lift the activation button or mechanism smoothly.
5. Confirm that the magnetic unit is fully released.
6. Remove the magnet carefully.
7. Clean it before storage.

Do not release the unit by striking the activation button with a hammer or forcing tools under the housing.

Impact and improper leverage can damage:

• The switching mechanism
• The housing
• The magnet assembly
• The casting table
• The release button

A purpose-designed release tool improves operator safety and extends equipment life.

Cleaning Shuttering Magnets

Concrete buildup is one of the most common causes of reduced performance.

Fresh concrete should be removed before it hardens. Once cured, concrete residue can be difficult to remove without damaging the magnet.

During cleaning:

• Use suitable non-damaging tools.
• Avoid striking the magnetic face.
• Do not grind the housing unnecessarily.
• Keep water and debris away from internal components.
• Check the button and spring movement.
• Apply suitable release treatment only where approved.

The bottom contact face deserves particular attention. Even a thin layer of hardened concrete can create a gap that reduces holding force.

Maintenance and Inspection

A regular maintenance routine should include:

Daily Checks

• Remove concrete residue.
• Inspect the contact face.
• Check activation and release.
• Look for visible damage.
• Confirm smooth operation.

Scheduled Checks

• Inspect the housing for deformation.
• Check the release button and mechanism.
• Inspect welds and fasteners.
• Test holding force if required.
• Check adapters for bending or wear.
• Review unusual formwork movement.

Periodic Performance Testing

A pull test can be used to compare the magnet against a baseline value.

For consistent results, use:

• The same steel test plate
• The same pull direction
• The same test fixture
• A calibrated force gauge
• A clean contact surface
• A stable test temperature

Performance records can help identify gradual deterioration before it causes a production problem.

Common Causes of Reduced Holding Force

Concrete on the Magnetic Face

Concrete creates a gap and prevents full contact.

Thin Casting Table

The steel plate may be unable to carry all the available magnetic flux.

Uneven Contact

Warping, weld spatter or damaged surfaces reduce the effective contact area.

Incomplete Activation

The mechanism may not be fully engaged because of debris or damage.

Excessive Temperature

Exposure above the design limit can reduce magnet performance.

Internal Mechanical Damage

Impact, water entry or worn components may affect the magnetic circuit and switching mechanism.

Incorrect Testing

A result measured on a different steel plate or under different conditions may appear lower even when the magnet has not changed.

Storage Recommendations

When shuttering magnets are not in use:

• Clean and dry them.
• Store them in the released position unless instructed otherwise.
• Keep them away from excessive heat.
• Protect the contact surface from impact.
• Avoid stacking them in an unstable arrangement.
• Keep them away from sensitive electronic devices.
• Use suitable spacing or storage racks.
• Do not expose them to standing water.

A dedicated storage rack can help prevent magnets from attracting one another or attaching unexpectedly to nearby steel equipment.

Operator Safety

Shuttering magnets can generate strong attraction and should be handled carefully.

Potential hazards include:

• Pinched fingers
• Sudden attraction to steel
• Collision between magnetic units
• Heavy manual handling
• Flying steel tools
• Damage to electronic or medical devices

Basic precautions include:

• Wear appropriate gloves.
• Keep hands away from the contact area.
• Use the correct handling and release tools.
• Do not place loose steel tools near an activated magnet.
• Keep magnetic units separated during transport.
• Follow site rules for people with implanted medical devices.
• Train operators before the system enters production.

Strong shuttering magnets should not be treated like ordinary steel boxes.

When Is a Custom Shuttering Magnet Required?

A standard shuttering magnet may not suit every formwork system.

Customization may be appropriate when the project requires:

• A non-standard holding force
• Restricted installation space
• A special housing shape
• A customized activation button
• A specific adapter connection
• An integrated formwork profile
• High-temperature operation
• A specialized casting table
• Automated handling
• A project-specific pull test

WZ Magnetics Co., Ltd. can evaluate the magnetic circuit, housing structure and adapter interface according to the customer’s production line.

Information to Provide With an Inquiry

For a more accurate recommendation, provide:

1. Precast concrete product type
2. Formwork material
3. Formwork height and length
4. Concrete pouring height
5. Concrete consistency
6. Pouring and vibration method
7. Proposed magnet spacing
8. Casting table material and thickness
9. Available installation space
10. Adapter or profile drawing
11. Required nominal holding force
12. Quantity
13. Expected operating cycle
14. Testing requirements

Photographs or videos of the current formwork setup can help identify practical installation issues.

Shuttering Magnet Selection Checklist

Before confirming a magnetic shuttering system, check that:

• Concrete pressure has been considered.
• The magnet rating matches the expected load.
• The casting table is sufficiently thick.
• The table surface is clean and flat.
• Magnet spacing is appropriate.
• The adapter fits the formwork profile.
• The load does not create excessive leverage.
• Operators have the correct release tool.
• Cleaning access is available.
• Safety procedures have been established.
• Trial casting has been completed.
• Maintenance and testing intervals are documented.

Shuttering magnets can make precast concrete production faster and more flexible, but their performance depends on the complete formwork system.

Rated holding force is only the starting point. Formwork height, fresh concrete pressure, vibration, magnet spacing, adapter design and casting-table condition must all be considered.

For reliable operation:

1. Choose a magnet based on the actual casting process.
2. Match the adapter to the formwork profile.
3. Keep the magnetic face and casting table clean.
4. Use the correct activation and release tools.
5. Confirm the arrangement through trial casting.
6. Maintain and test the magnets regularly.

 

 

WZ Magnetics Co., Ltd. manufactures standard and customized shuttering magnets for precast concrete production. Send us your formwork drawing, casting-table specification and production conditions for an initial technical evaluation.

Frequently Asked Questions

What is a shuttering magnet?

A shuttering magnet is a switchable permanent magnetic assembly used to secure precast concrete formwork to a steel casting table.

How do you choose the correct shuttering magnet?

Selection depends on formwork height, fresh concrete pressure, vibration, magnet spacing, adapter design and casting-table condition. Nominal holding force alone is not enough.

What holding force do I need?

Low formwork may use a smaller force class, while tall or heavily loaded forms require stronger magnets or closer spacing. The required force should be calculated for the actual production conditions and verified through trial casting.

Why has my shuttering magnet lost holding force?

Common causes include concrete residue, thin steel, uneven contact, incomplete activation, mechanical damage or excessive temperature.

Can shuttering magnets be used on any steel table?

The table must be made from a suitable ferromagnetic material and have adequate thickness, flatness and structural support.

How far apart should shuttering magnets be placed?

Spacing depends on the stiffness of the formwork, concrete pressure, vibration and required dimensional accuracy. It should be confirmed through calculation and trial production.

Can shuttering magnets hold wooden formwork?

Yes. An adapter can connect the shuttering magnet to wooden formwork. The connection must be strong enough to transfer the expected load.

How should concrete be removed from the magnet?

Remove fresh concrete with suitable non-damaging tools before it hardens. Avoid striking, grinding or damaging the magnetic contact face.

How often should shuttering magnets be tested?

Inspection should be performed regularly, while formal pull testing can follow the factory’s maintenance and quality plan. The same test method should be used each time.

Can WZ Magnetics make custom shuttering magnets?

Yes. WZ Magnetics Co., Ltd. can customize the holding force, housing, dimensions, activation structure and adapter interface for different precast formwork systems.