I got a quote for replastering my pool but ended up repainting instead. I was told the way this company does it is to chip out plaster below the tile line so that the new plaster meets up with the tile and then sandblast the rest to remove the paint and rough up the surface, then they replaster.

I was also told by the contractor who painted my pool that you only need to replaster if the plaster is crumbling or falling off in chunks. If it is more of a cosmetic issue you can just repaint every 5 yrs or so.