Bonded vs Unbonded Screeds: Technical Differences and Application with SCREED X / FORCEM

Introduction

Screeds form the foundation for tiling and waterproofing systems. Correct specification between bonded and unbonded screeds is essential to ensure performance, structural stability, and compliance with AS standards.

Bonded Screeds

A bonded screed is applied directly to the substrate, typically over a water-based or cementitious waterproofing membrane such as ACTFLEX 906 WPU.

• Minimum Thickness: 10–15mm at the lowest point.

• Advantages:

  • Fully integrated with the substrate (becomes part of the slab).

  • Suitable for thin repairs, ramps, and overlay systems.

  • Less prone to lifting or hollow sounding areas when applied correctly.

  • Faster curing and less material consumption.

Bonded screeds are ideal for internal wet areas and applications requiring thin build-up while maintaining structural performance.

Unbonded Screeds

An unbonded screed is separated from the substrate by a solvent-based membrane or slip sheet. Because the screed is not adhered to the concrete, it is considered structurally “loose.”

• Minimum Thickness: 40mm at the lowest point.

• Reason for Thickness:

  • The screed requires self-supporting strength to withstand movement without cracking.

  • At <40mm, the screed lacks integrity and is more prone to shrinkage cracks and debonding.

• Applications:

  • Over slip membranes where substrate bonding is not possible.

  • Roof slabs or external areas using solvent-based membranes.

Unbonded screeds are designed to provide durability, impact resistance, and load stability where direct bonding cannot be achieved.

SCREED X and FORCEM in Practice

Both SCREED X and FORCEM products are engineered for use in bonded and unbonded screed applications:

• As a bonded system, they ensure adhesion to the substrate and become part of the slab structure.

• As an unbonded system, when placed at 40mm+, they provide the compressive strength and flexibility required to resist cracking and movement.

Conclusion

Choosing between bonded and unbonded screeds is not just about thickness — it’s about understanding substrate interaction, membrane type, and structural integrity.

• Bonded Screeds: 10–15mm minimum, water-based membranes like ACTFLEX 906 WPU, fully integrated.

• Unbonded Screeds: 40mm minimum, solvent-based membranes or slip sheets, structurally independent.

For compliance and performance, SCREED X and FORCEM provide proven solutions across both systems.