How do you mortar/render/plaster a concrete surface?

Not a professional, but I've managed a lot of jobs dealing with concrete, so here is my recommendation. First, the surface of the existing concrete needs to be roughened to provide a profile for the mortar to stick to. Use a chipping hammer with a bushing head in it. Then skip the middle coat of sand and cement. Go to the hardware store and get a concrete bonding agent and apply to manufacturer's recommendations, then apply your coating of mortar mix. Mortar should not be runny, but more like peanut butter when you apply it. Cure the mortar by keeping wet with damp cloths.