Behind the spots
I dug at one of the spots with my fingernail and found this gloppy black tarry like substance. I did some research and found cases where the plasticizers in caulk and flexible PVC (which is what our rainscreen is made from) interacted badly with window wrap tape and essentially liquified it.
After many frantic phone calls to WRGrace, Ben Obdyke, and OSI Quad (makers of the flashing tape, rainscreen, and caulk respectively), we determined that in all likelihood, this was simply the solvents in the caulk leaching some asphalt out of the felt paper and window wrap. The Quad folks told me that now that the caulk had cured and solvents had evaporated, there would be no more problems. I observed the spots for about a month and they didn't change at all. I also noticed that where the caulk came in contact with the asphalt screen porch roof, it was completely brown yet the roof and caulk were unaffected, so that reassured me that the tape, caulk, and rainscreen were intact and functional.
After many frantic phone calls to WRGrace, Ben Obdyke, and OSI Quad (makers of the flashing tape, rainscreen, and caulk respectively), we determined that in all likelihood, this was simply the solvents in the caulk leaching some asphalt out of the felt paper and window wrap. The Quad folks told me that now that the caulk had cured and solvents had evaporated, there would be no more problems. I observed the spots for about a month and they didn't change at all. I also noticed that where the caulk came in contact with the asphalt screen porch roof, it was completely brown yet the roof and caulk were unaffected, so that reassured me that the tape, caulk, and rainscreen were intact and functional.
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