Broken bolts - Water pump

[totta Crolla]

As it happens I was talking to a specialist welder chap today and he was showing me some of his work and one piece was a recessed snapped bolt with an 'easy out' broken off inside ('easy out' is the super hard but brittle left hand threaded hateful affair mentioned above) the owner of the piece had given up on it as it was also now impossible to drill out.
The welder guy got some copper tube the same outside diameter as the 13mm bolt and Nickel welded enough material onto the bolt through the inside of the tube to enable a nut to be welded on. It then unscrewed ok.
He said the key was to build up the weld gradually and use special nickel wire.