Precast concrete that is generally blemish free raises the stakes considerably when it comes to delivering a top class repair. The same could be said for self compacting in situ concrete.
Whilst as with any remedial work the key starting point is flush, true and texture appropriate filling, colour matching such good original work up’s the anti to dizzy heights. Achieving a close colour match in terms of tone is not an issue per se. It is the successful diffusing of minute tonal variation to convince the eye to believe.
If the concrete is pre cast or site batched in steel shuttering then this adds a significant advantage as the surface quality of steel formed concrete tends to have a nice balance of light reflectivity. Not too shiny and not too dull.
The images here are the before and after of construction damage on a pre cast column for BP. It is irrelevant to the repair process but it is probably a PFA blended mix. The blotchy marks have come from differential curing not the casting p...
The reality of site work is that no matter how fluid the communication is between all contractors and sub-contractors, some form of construction damage will probably happen. This type of damage is usually to arris edges especially where installation of doors is concerned. Another popular place is on exposed soffits from scaffolding and so on. Misplaced drill holes, or drilling through the back of a wall and taking a good old chunk out of the front is another favourite. If any construction damage is going to happen anywhere, the best place is on an arris edge. Arris edges have the advantage that they form a junction between two faces and there is a natural line of the edge for the eye to follow up and down and get distracted by. If a door frame is installed it's even better. This makes the repair much more forgiving. The general rule of thumb is that is a repair is close to any kind of junction (edge, soffit, floor, arris, tie hole etc. then half the battle is already won.