Thanks, TimR. Pretty sure drywall mud, etc. would not cling to a vertical pipe...

Are you saying lime scale would not be that thick or easy to scrape? What would you expect with lime scale? (This stuff was the texture of frosting mixed with sawdust.)

Also, maybe it's possible wax from the ring may have been in the mix, but it didn't look waxy/greasy/shiny at all.

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