I think you only need the Lime if you need to match existing pointing.
Tell him to put some washing up liquid in the mix, it might be that he's worked it for too long and it's started to go off before he's finished.
Putting the washng up liquid in will give him more time to work with it.
It's also worth remembering that the brickwork should be wetted before applying the pointing, otherwise the bricks just soak all of the water out of the mix.
<Edit: Dang, marky beat me to it
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There's some more good advice here:
http://www.diydata.com/techniques/br...g/pointing.htm