Alternatively you can do a plywood substrate as a detail also; this is obviously more expensive but similarly helps to "cushion" the flooring's feel when it is walked on. If you put the finish material directly on the slab with no substrate (foam, wood, whatever), it is going to be VERY uncomfortable to walk on / stand on for extended periods of time. It'll have a very low thermal protection value also (not that we in LA care too much about that
).