Results 1 to 9 of 9
  1. #1
    Join Date
    Apr 2005
    I would like my contractor to insulate and seal the hard duct that will replace the existing flex duct in my crawl space. I mentioned mastic to two contractors. One seemed not to be familiar with mastic but said he could use a hvac caulk. The other seemed reluctant and when he submitted his estimate he specified that he woud tape the joints. I assume he will use foil tape. In other old posts I have seen a wide variety of opinions on foil. Is there a foil tape that won't fail after a few years? Is there a mastic tape that is really durable? Can insulation be pulled over wet mastic? Does caulk work?

  2. #2
    Join Date
    Sep 2004
    Is there a foil tape that won't fail after a few years?

    there is a foil tape that is next to impossible to get apart 5 minutes after it is applied, I would say it will hold up after much more than a few years

    same holds true with mastick and caulk

    Can insulation be pulled over wet mastic?

    yea , you can pull it over wet mastic, it will stick and get it everywhere, mastic may not dry

    Does caulk work? of course it does . they wouldnt make it if it didnt work

  3. #3
    Join Date
    Sep 2001
    Vancouver Canada
    Foil tape if he is just sealing joints and such, mastic is just way to messy for my liking. I like to use caulking on the units as I can use a gun and get a nice bead.
    "Go big or Go Home"

  4. #4
    Join Date
    Feb 2003
    How about the seams & cracks & holes in the plenums/ boxes?
    I prefer mastic = messy --

    My 1974 duct tape is still GOOD = will not strip off, have to cut it & scrape! not a clue as to what brand --

  5. #5


    Foil tape that will duct peel off in a few years is Hard Cast (POOKIE TAPE). Pookie Tape is thicker than foil tape and stay stuck as long it isnt flue pipe.

    Other duct sealant is MV181 is a water based mastic type duct sealant that you dont have to use mummy bandage like with mastic or air ball.

    Silicon is okay but it needs to low fume and not translucent to pass IMC regulations.

    Insulation can be added to any wet sealant.

  6. #6
    Join Date
    May 2002
    I understand duct mastic has been proven to hold up better than any tape. Unfortunately some installers spread it on a little too thin.

    If you use aluminum tape, use only tapes that are stamped in red with UL181A and UL181B. Those tapes use an acrylic (I think) mastic that holds up much better at forced air heating temperatures than cheaper tapes that use rubber-based mastics. Some tapes are stickier at first, but apparently fail much sooner.

  7. #7
    Join Date
    Nov 2000
    Coastal Georgia

    Caulk is for tile and windows. Foil tape needs a good clean and oil free surface and most of all applied with pressure. Mastic is O>K but I have tried the mastic tape and it is great.

  8. #8
    Join Date
    Apr 2005


    Thanks for the replies. Guess my contractor isn't the only one who doesn't like mastic.

    ct2 Can you tell me the name of the very sticky foil tape. If my contractor won't use mastic maybe I can get him to use a high performance foil tape.

    Black Adder What brand and type of caulk do you use for ducts?

    Deanoac Are you saying that hardcast pookie tape tape will not peel off? I assume Hardcast makes it.

    James Who makes mastic tape and is there one that you like. I am pretty sure my contractor is not aware of mastic tape since he didn't mention it. Where is it sold?

  9. #9
    Join Date
    May 2000
    Colorado flatland native
    My roll says.......

    Hardcast by Carlisle
    My doctor gave me six months to live, but when I couldn't pay the bill he gave me six months more.
    Walter Matthau

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