Repairs to concrete are easy to conceal, provided that you take care to match the finish to the existing surface texture.
The occasional crack in a concrete path can occur for various reasons and it is simple to fill in the damage. However, where there are numerous cracks and depressions the cause is likely to be poor foundations in which case there is little alternative but to break up the concrete and start again from scratch.
For an occasional crack use a mix of 1 part cement to 3 parts sand or buy a suitable bag of dry-mixed cement mortar. In either case it is well worthwhile adding a little PVA adhesive to the mix; this acts as a bonding agent to ensure a firm grip between the old and the new concrete. Check the manufacturer’s instructions for exact details for using the adhesive.
Use a cold chisel and club hammer to undercut the crack — this forms it into an inverted ‘V’ shape with the point of the ‘V’ at the surface. The filling material will then be well anchored. Clean all dust from the crack and then brush a coat of diluted PVA adhesive on to the crack to serve as a primer. Provided that the repair mix is on the dry side it will be easy to pack it down well into the crack and to level it off with the surface. Sometimes a steel float makes it easier to leave a level finish.
Holes in the surface are mostly found near cracks. They can be caused by weak foundations too (if there are several the concrete mix may have been too weak). Repair them as for cracks.
These are often caused by removing the formwork before the concrete was fully hardened. Another possibility is that the concrete mix was not pushed well down into the edges, leaving an air pocket below the surface.
Break up the crumbling edge with a cold chisel and club hammer, going back to firm material. Remove loose material and tamp down the foundations, adding new hard-core if needed. Set up a formwork alongside the repair and brush PVA adhesive on to the exposed edge. Mix up a batch of 1 part cement to 5 parts ballast (or use a bag of dry-mix) and add a little PVA adhesive. Press the mix well down into the edge of the formwork. Allow four weeks before removing the formwork.
Hollows where puddles form can be filled successfully only if they are more than about 12mm deep. If less than this, the area will have to be broken up and relaid. Repair the hollow using the mix and techniques specified for cracks. Formwork is needed if the edge of the concrete is affected.