Renew a broken edge of a concrete step by first chipping away all the loose concrete. Chip out about 25-37 mm 1-1.5. in of the step, undercutting the edges with a bolster. Place a board against the front face of the step and hold it in place with bricks – making sure that the top of the board is flush with the top of the step. Coat the edge with a PVA bonding agent to stop the existing concrete absorbing too much moisture from the new mix.
Mix one part of cement with three parts of coarse sand and. Using a trowel, apply the mortar, forcing the mix into the undercut edge. Smooth off the surface with a wooden float, so that the concrete will dry out to a slightly roughened finish.
Remove the board after about six hours, but avoid stepping on the repair for at least a week. If the weather is hot, cover the repair with damp sacking.