.

No basements here either, but from the looks of it, like Rick said, it appears to be seeping through up from inside the tackless strips.

I'm guessing that the footing was poured, the basement foundation walls placed and poured on top of the footing, then the basement slab poured inside the inside perimeter of the footing, leaving a cold joint, and an unsealed joint, all the way around the basement inside edge of the footing where the slab was poured to.