about a month ago, i installed about 500sf of armstrong natures gallery and 2 in 1 quiet step over a concrete slab. everything looked great for a couple of weeks, then i noticed a gap had developed in the planks. it's about 7 ft long and 1/8 to 1/16 wide. it's gradual, going from being locked together at each end. it covers several boards. a week later, i found another area with a gap (this time about 5 feet long). is anyone else experiencing this problem? i don't want to take half the room apart, but i can't seem to force the pieces back together. any ideas?