Hello...I'm so happy that this message board is up and running. What a wonderful resource! About 3 weeks ago we had an engineered maple floor installed in our living room. It was glued onto concrete. Today my mother in law was visiting and she pointed out that a particular section of the floor sank slightly under her weight . My husband and I later noticed the same thing when we walked on it. We knocked on the floor and noticed that that section sounded very hollow compared to the rest of the floor. The general contractors are still here finishing up our remodel so I want to mention any potential problems now before I pay the final payment. Any thoughts or educated guesses as to what the problem might be?

Sounds like a lack of floor prep to flatten the substrate to the strict tolerance specifications.

Lay a straight edge across the floor and it will tell you if the floor is heaving, or if it is flat but just sinking in a low spot in the substrate.