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cp-10/cp-11 mastic really necessary for steam pipe insulation?

swiharta Member Posts: 2
edited November 2020 in Strictly Steam
Is applying this mastic really necessary for exposed portions of fiberglass insulation placed on steam pipes? There should not be any condensation on the outside of the pipe, correct? So is the benefit just cosmetic? I would like to insulate the straight runs with pre-formed pipe insulation with ASJ and get to elbows and tees later. I'd rather just leave off the mastic if it isn't important.

And if there was a pipe leak, you would probably be better off having a way for water to get out so you notice the leak rather sealing up any exit points and soaking a larger amount of pipe and insulation.


  • swiharta
    swiharta Member Posts: 2
  • Jamie Hall
    Jamie Hall Member Posts: 20,525
    mastic? Mastic? What mastic. At least I've never used any... just snapped the insulation on, taped it up, and that was that.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 13,170
    No. You don't need the mastic. It is used as a vapor barrier on the fittings after the fitting covers are put on but is only needed when you insulate chilled water piping with fiberglass