How to Create a Clean Edge Detail for a Cast-In-Place Concrete Mould

Using Concrete Lab Products

When casting concrete worktops or surfaces in place, a clean and consistent edge detail can make all the difference to the finished look. At Concrete Lab, we often get asked how to form the edge profile neatly—particularly when casting directly onto a cement board base. In this post, we’ll walk through a practical method using easily available materials, including how to plan your edge profile and formwork to suit a 30mm thick concrete pour.

Start with the Right Base

We recommend using a 6 or 12mm cement board as your base for a cast-in-place project. It’s stable, moisture-resistant, and offers a good bonding surface. This cement board acts as the bottom of your mould and sits directly on your cabinet or framework.

Plan Your Concrete Thickness

For strength and durability, the concrete itself should be 30mm thick. So, depending on the thickness of your cement board, the total thickness at the edge of the worktop will be either:

36mm (with 6mm board), or
42mm (with 12mm board)

Make sure your edge form accounts for this.

Creating the Edge Form

To form a neat edge that can be removed cleanly after curing, follow this simple method using plywood and melamine:

1. Use Plywood as a Support Strip

Cut a strip of 18mm thick plywood, 50mm wide.
Fix this plywood strip to the underside of the cement board, so that it juts out 25mm beyond the edge. This overhang will support your vertical form and help define the outer edge of your worktop.

2. Attach a Vertical Melamine Strip

Cut a vertical strip of melamine board to match the total thickness (cement board + concrete) plus the plywood. So the melamine strip should be:
- 54mm high (if using 6mm cement board)
- 60mm high (if using 12mm cement board)
Fix this melamine strip to the outside face of the plywood, so it stands upright and creates the form for the concrete edge.
Melamine is ideal here because its smooth surface allows for an easy release and a clean finish on the edge of the concrete.

Pouring the Concrete

Now it’s time to pour. Concrete Lab’s Self-Compacting Concrete Cast-In-Place Mix is perfect for this type of application. Because it doesn’t require vibration, it’s ideal for cast-in-place projects where formwork might be fixed in tight spaces.

Mix and pour the concrete as per our instructions to a consistent 30mm thickness, ensuring it reaches all corners of the form and settles flat against the base.
Use a straightedge to level the surface, and trowel the surface.
Once cured, remove the vertical melamine strip, then unscrew and remove the plywood support.

Finishing the Edge

You should be left with a sharp, smooth edge that follows the exact profile of your melamine strip. Any minor imperfections or pinholes can be filled using Concrete Lab’s Smoothing Paste—a colour-matched, cement-based filler designed for a seamless finish. Apply it across the edge if needed, allow it to cure, then sand lightly for a flawless result.

Summary

This method provides a reliable, repeatable way to form cast-in-place concrete edges with precision. By using:

A 6 or 12mm cement board base
Concrete Lab’s Cast-In-Place Mix
A removable plywood/melamine edge profile

…you can achieve clean lines, sharp corners, and a polished final look.

Need help selecting the right products or tools for your project? Why not use our handy project calculator to work out the quantities and ancillary products for you - Cast-In-Place Project Calculator.

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