I have managed to get 2.5mm T&E through many battens in a dry lined wall. It has gone past a few sharp nails inside the wall which has scratched the grey outer cover in places. The worst scratch very slightly shows some blue of the inner cable (less than 1mm - no bare wire is showing, the blue is intact). Is it OK to wrap a piece of spare grey outer around it and gaffer tape & to carry on? (it is half way round and took hours to get there!)