I’ve installed pre-finished hardwood flooring on top of a concrete slab and I’m experiencing cupping and cracking. I installed 3/4″ cdx plywood to the slab first, then ran 15# felt on top of that before nailing the flooring down. Some areas are fine, so I don’t think it is a product or installation issue. I believe it is excess moisture coming through the slab, but thought that the felt should have helped with that. Is there any thing that could be done instead of the described method that will not just create another problem?

Thanks in advance for any input!