Rendering. how to repair / what type of mix

I need your help to repair some external rendering on walls (not the house). The rendering is either blown or seriously cracked (movement as the walls adjoin the street).
What is the best way of repairing it and with what type of mix? Do I need a sealer / glue on the bricks before adding the first coat of render? What is the mix of the first coat, do I need some lime? What is the mix for the top coat? How long does it for the rendering to dry? Does Wickes sell the stuff that I need?
Thanks for any help
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