How to Create a Downstand (Lip) for GFRC Concrete Worktops

What is a Downstand?

When casting precast concrete worktops, a downstand (or lip) is often used to create the look of a thicker slab without adding unnecessary weight. The downstand makes the worktop appear chunky and bold, while the base remains a practical thickness for handling and installation.

Recommended Thicknesses

• Base: Always cast at 18–20mm thick. This is strong enough for flipping and finishing, while keeping the piece light.

• Downstand up to 70mm high: 20–25mm thick. No reinforcement required.

• Downstand 70–100mm high: 20–25mm thick with austenitic screws set into the base during casting for extra support.

• Downstand over 100mm high: Increase thickness to ~30mm and use longer austenitic screws to securely tie the lip to the base.

Why Thickness Matters

The weakest part of any downstand is the connection between the lip and the base. If the lip is too thin, knocks or impacts can cause it to crack or de-bond over time. Making the lip slightly thicker — and tying it back to the base with screws — keeps the joint solid and prevents issues in service.

Practical Casting Tips

• For open moulds (no lid):

  • Pour the base first, then let it firm up.

  • Set stainless screws into the base where the lip will be cast.

  • Pour the lip once the base can hold them in place.

• For taller lips (>100mm):

  • Make the lip 30mm thick.

  • Use longer screws so the lip is firmly locked into the base.

• Always think about how the concrete will flow into tall, narrow sections. Going too thin on a 150mm lip will make voids more likely.

Summary

By following these guidelines, you can achieve the chunky “thick slab” look with your GFRC worktop while keeping it light, practical, and durable:

• Base: 18–20mm

• Lip up to 70mm: 20–25mm, no reinforcement

• Lip 70–100mm: 20–25mm + screws

• Lip over 100mm: 30mm + longer screws

👉 For more guidance and materials, explore the Concrete Lab GFRC Worktop Mix and our full range of tools and finishes.