Cardboard Void Former

A concrete void former is a formwork material placed under concrete slabs to create a controlled cavity between the ground and the concrete. It temporarily supports the wet concrete during pouring, then degrades to form a void, reducing the risk of soil heave impacting the slab.

Void formers in concrete slabs are commonly used in residential and commercial foundations built over reactive clay soils. They are also used in civil, infrastructure and industrial projects where ground movement is a concern or where slab separation is specified in the engineering design.

• Weight reduction: Critical for large spans, reducing foundation and structural load
• Cost savings: Less concrete is required, lowering material and transport costs
• Improved design flexibility: Enables longer spans and thinner slab profiles
• Thermal efficiency: Voids can improve the insulation properties of the slab system
• Sustainability: Many systems incorporate biodegradable or recyclable components

We offer same-day dispatch Australia-wide for stocked void former products. Customers can also arrange convenient call-and-collect orders directly from our Melbourne or Sydney warehouses that operate from 6.30am - 4.30pm Mon-Fri. Orders placed after 4.30pm (AEST) can be collected next-business day after 7.30am.

Void formers are available in several forms, including cardboard void former systems, expanded polystyrene (EPS) and polymer-based systems. Some are designed to collapse or compress under pressure, while others degrade over time to form a true void. The best choice depends on the engineering design and soil conditions.

The appropriate void former depends on factors such as soil reactivity, slab load, required void depth and project specifications. It's important to consult your engineer or site designer. Allcon can assist with product selection and provide guidance based on your project’s needs.

Yes. Void formers can be used in combination with under-slab insulation or XPS foam where thermal performance or moisture control is required. Layering must follow engineering specifications to maintain void integrity and insulation value.

Void formers should be stored in a dry, well-ventilated area away from direct sunlight and moisture. Exposure to rain or high humidity before installation can compromise structural integrity, particularly for cardboard void formers and other biodegradable systems.

For tailored advice on selecting and installing void formers, contact Allcon or speak with our technical team. We’re here to help you choose the right void solution for your next project.