Q: I recently put down P—- laminate flooring that has a backing on it, no underlayment, concrete floor is 20 years old. Now the floor pops and cracks.
A: Possibly some expansion happening. Did you leave a gap around the perimeter? Was the concrete flat? You could place a hygrometer on the floor and see what kind of humidity reading you get. If it is very high, say 65% or more, dehumidify.