The problem I was faced with was 6 large anchor bolts fitted in the wall. The drill hole to originally fit these was 14mm, the hole depth was about 120mm. The stud (left in the photo) was 10mm. As I did not drill the holes particularly deep I could not simply knock them in and hide the sins with filler, so my only option was to extract.
I tried all suggestions on the Internet to remove these to no avail.
After my success (all credit must go to my cousin for the idea and his rich tool set) I thought the least I could do was post this to hopefully help others in the same predicament..
Throughout, I refer to the two parts of the anchor fittings as the anchor bolt and anchor shield.
Step one: Extract the anchor bolt stud as far as possible by tightening the nut and washer against the wall. When done gently remove the nut and washer.
Step two: Angle grind the anchor bolt hanging out the wall, while doing this clean up the anchor shield in preparation for a good weld.
Step three: Knock the bolt in as far a as possible with the hammer and punch. Ensure the anchor shield stays put.
Step four: Offer up the suitably sized stud (12mm in this case). Thread this into the anchor shield, that is if the anchor bolt is buried enough, if not, this can simply be held in place using the earth lead clamp of the welder during the weld process.
Step five: Use the mig welder (or similar) to attach the short piece of stud (like in the photo) to the anchor shield.
Last step: Use the 12mm nut and washer to fix the stud to the slide hammer and start hammering, watching those fingers..
We were able to remove all 6 bolts in just a few hours. The slide hammer seemed to remove most of these with ease (only one real stubborn one but the weld held strong). If you don't have access to a slide hammer, you could weld a longer stud to it and use a block wood drilled with an over sized hole and simply extract by tightening a washer and nut onto this.
The photo shows (from left to right) the extracted anchor bolt and the anchor shield with the 12mm stud attached by the weld joint.
Slide hammer (ideal but not necessary)
Threaded studding (12mm in my case)
12mm nut and washer