I don't mean to hijack this thread, but thought my question (if answered) might help at this point. When I scraped my old caulk away, from roof penetrations (skylight and fan) and the awning rails, the caulk was sort of crumbly. It reminded me of very old window glass glazing putty. It was, for the most part, still white. When I went to remove the caulk around the plumbing stack- well, that was a different story. It was discoloured (black) like Robert's classic photo. It was also very much still elastic, and sticky. I needed to use the heat gun on this stuff, whereas I did not on the other.
So, who can say what were these two very different sealants? And is it really necessary to use two types?
All kids are gifted; some just open their packages earlier than others. - Michael Carr