Quick Answer

Smooth concrete edges with an angle grinder and a diamond cup wheel or a coarse flap wheel, working at 45 degrees along the edge and blending into the face. Start with 16-25 grit to remove the sharp arris, then step to 80-120 grit to blend the transition so the edge looks intentional rather than just knocked off.

Why Edges Need Grinding After Forms

Form edges are sharp, sometimes honeycombed, and rarely perfectly straight. Grinding the arris removes the weak, brittle corner that chips easily and creates a clean, chamfered look. It also reveals any honeycomb or surface voids early, when a patch is still practical, instead of after the concrete fully cures.

Tools for Edge Work

An angle grinder with a diamond grinding cup wheel is the standard setup: the cup wheel reaches the edge flat and removes material fast. For a finer finish use a 80-120 grit disc. On very long edges, a floor grinder with a smaller head or a dedicated edge machine works faster, but the angle grinder is right for stairs, curbs, and slab perimeters.

Grinding Technique for a Clean Chamfer

Hold the grinder at about 45 degrees so the wheel cuts the arris and the face evenly. Move in one continuous direction along the edge, overlapping each pass. Do not rock the grinder; keep the wheel flat against the chamfer. Work from the ends toward the middle, and check the chamfer size with a template or your eye against the straight edge. Stop before you round the edge into the face.

Safety and Dust Notes

Edge grinding throws concrete fragments and silica dust. Wear eye protection, a respirator, gloves, and hearing protection. Use a dust shroud with vacuum where possible. Keep the grinder guard on, check the wheel for cracks before mounting, and let the tool do the work with light pressure near the ends of the edge.

Frequently Asked Questions

Q: How big should the edge chamfer be?

A: A 10-15mm chamfer looks clean on most slabs. Match it around the whole perimeter so it is consistent.

Q: Can I smooth edges with sandpaper?

A> For fine touch-up yes, but sharp arrises need a diamond wheel first. Sandpaper alone will not remove concrete fast enough.

Q: What if the edge is honeycombed?

A: Grind out the loose material until sound concrete is exposed, then patch with a repair mortar before finishing the chamfer.

Conclusion

Form edges become clean chamfers with a cup wheel and a steady 45-degree pass. Grind the arris, blend with a finer grit, and protect the edge from chipping with consistent technique all around the slab.