Never seen this.
If you think it is plumbing or radiant heat pipes, pressure test the pipes.
If you want to check for moisture, there are a couple of options.
Following are several industry-recognized concrete slab moisture tests that provide measurement of emission rate:
- Polyethylene Film Test
Tape a 2’ x 2’ square of 6 mil. clear polyethylene film flat to the slab, sealing all edges with moisture resistant tape. Suspend a 250-375 watt heat lamp 2’ above the plastic film. After 24 hours, check the film – if no condensation or “clouding” develops on the underside of the polyethylene, the test area shall be considered dry enough to install wood flooring.
- Phenolphthalein Test
Apply several drops of a 3 percent Phenolphthalein solution in grain alcohol at various spots on the slab. If a red color develops in a few minutes, the slab is too wet to begin installation of the finished flooring system.
- Calcium Chloride Test
Use a prepackaged calcium chloride test (widely available) and follow the manufacturer’s instructions. The Calcium Chloride Test measures the quantity of moisture passing through a concrete floor. This measurement is stated as pounds of moisture over a 1,000 sq. ft. area during a 24-hour period. An acceptable level is 4.5 lbs. or less.
Wrong adhesive bleed through, might be another possiblity.
Hope this helps.