Slab Formwork Methods: Table, GRIDFLEX and Conventional

Formwork is not a single construction method. On a concrete structure, the most suitable system depends on the floorplate, repetition, slab depth, programme, crane access, labour, temporary works design and the amount of irregular detailing around edges, beams, cores and penetrations.

For that reason, experienced formwork teams rarely think in terms of one system being universally "best". The better question is: which method gives this project the right balance of speed, accuracy, flexibility and safe execution?

Three approaches commonly encountered in slab construction are table formwork, GRIDFLEX grid-element formwork, and conventional timber and plywood formwork. Each has a different strength, and on many projects they are used together.

What slab formwork actually has to achieve

Before comparing systems, it is worth remembering what the formwork is doing.

During a pour, the deck and its supporting structure must hold wet concrete, reinforcement, workers, equipment and construction loads while maintaining the required geometry. It must establish slab levels, edges, beams, set-downs, openings and other structural details accurately enough for the finished concrete to meet the project requirements.

The system also has to work as part of a construction cycle. It must be erected, checked, poured, struck and moved in a controlled sequence while the structure develops sufficient strength.

This is why system selection affects much more than carpentry. It influences labour, crane movements, floor-cycle time, logistics, concrete finish and the amount of adjustment required by the trades that follow.

1. Table formwork: built for repetition and floor-cycle speed

Table formwork uses large pre-assembled sections of slab formwork that can be struck and moved as complete or substantially complete units. Rather than dismantling the deck into individual joists, bearers and sheets after every pour, the table is transferred to its next position and reused.

That makes table systems particularly effective on multi-storey buildings with large, repetitive floorplates.

Where table formwork performs well

Table formwork is well suited to projects where:

• floor layouts repeat from level to level;
• there are sizeable open slab areas;
• the programme benefits from a consistent floor cycle;
• the site has suitable crane or table-moving logistics;
• the project team can standardise table sizes and movement paths.

Once a table layout has been planned properly, the repetition can produce a very efficient rhythm. Teams become familiar with the sequence, fewer individual components need to be rebuilt each cycle, and the deck geometry can be reproduced consistently from floor to floor.

The main advantages

The strongest advantage is repeatability. Large deck areas can be formed using assemblies that have already been built and adjusted.

Other benefits can include:

• reduced dismantling and rebuilding between floors;
• consistent deck geometry;
• fewer loose components in repetitive areas;
• efficient use of labour on large floorplates;
• fast movement when the building and lifting strategy suit the system.

Where tables need support from other methods

No building is made only from perfect rectangles.

Columns, cores, slab edges, penetrations, balconies, transfer zones, changes in slab geometry and infill areas can all interrupt the table layout. These locations often require smaller system elements or conventional formwork.

Crane access and movement planning also matter. A table system can be highly productive, but only when the site logistics allow the units to be struck, moved and repositioned efficiently.

2. GRIDFLEX: a flexible grid-element slab system

GRIDFLEX is PERI's proprietary grid-element slab formwork system. Instead of relying on large pre-assembled tables, it uses lightweight grid elements supported on props, with form lining installed over the grid.

The concept provides a useful middle ground between large table systems and fully conventional formwork. It is modular and repeatable, but still adaptable around changing slab geometry.

Where GRIDFLEX is useful

GRIDFLEX can work particularly well where:

• slab areas repeat but are not perfectly uniform;
• the project needs a hand-set system rather than large crane-moved tables;
• there are changes in room or bay geometry;
• the team wants a modular grid that can accommodate infill areas;
• the floorplate includes a combination of regular and irregular zones.

Because the supporting grid defines the working pattern, the system can make the deck layout easy to understand on site. It can also reduce the amount of loose conventional framing required across the main slab area.

The main advantages

A grid-element system can provide:

• good flexibility across different slab layouts;
• lightweight components that can be handled in a planned sequence;
• repeatable prop and panel/grid positioning;
• adaptable infill around edges and irregular areas;
• reduced dependence on large table movements.

As with any proprietary formwork system, the actual configuration, slab capacity, prop arrangement, erection sequence and striking procedure must follow the project design and the manufacturer's requirements.

3. Conventional formwork: maximum flexibility for complex geometry

Conventional slab formwork is generally built from a combination of plywood or another form-facing material, timber or engineered beams, joists, bearers, props and supporting components.

It is the most adaptable of the three approaches because the formwork can be built around the exact geometry of the structure rather than asking the structure to suit a standard module.

Where conventional formwork remains the right solution

Conventional methods are particularly valuable for:

• irregular slab shapes;
• beams and deepened zones;
• slab steps and set-downs;
• curved or angled edges;
• one-off structural details;
• penetrations and congested service zones;
• ramps, stairs and complex transitions;
• infill between proprietary systems.

This adaptability is one reason conventional formwork remains essential even on highly systemised projects.

The trade-off

Flexibility comes with a cost in labour and planning.

A conventional deck may require more individual measurement, cutting, fixing, levelling and dismantling. Its productivity therefore depends heavily on the skill of the formwork carpenters, the quality of the set-out and the level of repetition available.

For a complicated one-off area, that extra effort is often justified. For hundreds of square metres of identical slab, a systemised method may be more efficient.

Table, GRIDFLEX or conventional: a practical comparison

The right choice is rarely based on speed alone. A system that is fast in an open area can become inefficient if the project has too many interruptions, while a flexible system can save time overall by reducing difficult transitions and rework.

The most effective solution is often a hybrid

Real projects frequently use more than one formwork method on the same floor.

A contractor might use tables through the main repetitive bays, a grid-element system through areas where the geometry changes, and conventional formwork around cores, slab edges, beams, penetrations and other non-standard details.

This hybrid approach allows each system to do the work it is best suited to.

The important part is coordination. The interfaces between systems have to maintain the same structural levels, dimensions and pour sequence. A fast main deck does not help if the edge details or infill areas become a bottleneck.

What should determine the system choice?

Before selecting a slab formwork method, the project team should consider the structure as a whole.

Floorplate repetition

Repeated geometry favours systems that can be reused with minimal alteration. The greater the repetition, the more value can be gained from tables or modular systems.

Structural complexity

Transfer slabs, beams, set-downs, unusual edges and dense penetrations increase the amount of custom work. Conventional formwork or adaptable infill may become more important.

Programme and floor cycle

The best system should support the intended sequence of forming, reinforcement, services coordination, concrete placement, curing, striking and reshoring or backpropping.

Site logistics

Crane availability, loading zones, storage, access and the ability to move equipment between levels can change which system is practical.

Labour and experience

A productive system still requires a team that understands how to erect, check, adjust and strike it properly. Familiarity with the selected method can make a major difference to performance.

Accuracy and finish

The chosen system has to deliver the specified slab level, dimensions and concrete finish. Connections, joints, deflection and form-facing condition all influence the result.

System selection is ultimately about buildability

The purpose of a formwork system is not simply to create a temporary deck. It is to help deliver the permanent concrete structure safely, accurately and efficiently.

Table formwork provides major advantages where repetition and movement logistics are strong. GRIDFLEX offers a modular grid with greater adaptability through changing slab layouts. Conventional formwork remains indispensable where the structure demands custom geometry and detailed carpentry.

A well-planned project uses these strengths deliberately rather than forcing one method into every area.

At USS Formwork, we approach formwork selection as part of the overall structural construction strategy. The aim is to choose and coordinate the system that best supports the geometry, programme, quality requirements and practical conditions of the project.