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Thread: Duct Mastic

  1. #1
    Join Date
    Jun 2005
    Posts
    77
    My attic duct consists of 9ea 6" Silver R6 ducts running off a 12 foot plenum made from Owens Corning 1 1/2 ductboard. The return is a 14" silver R6 flex.Everything is taped with the extra sticky wide silver tape. I had some of this tape that I thought was sticky until my installer showed me how much stickier his was.

    Anyway all my duct runs have the liner taped and tie-wrapped and then the insulation and silver cover is taped and tie wrapped as well. This may not be the best but its so much better than what I had for 18 years and that was keeping me nice and cool but after 18 years I wanted to upgrade

    If I wanted to go a step farther can I just mastic over what I have?? If so do I just paint the mastic right on the duct board, covering the tape all the way to the silver cover of the duct?

    Should I mastic all of the plenum joints including plenum to air handler??

    Is it runny or will it stay where I paint it?? I feel no leaks will it really help that much??

  2. #2
    Join Date
    Jan 2004
    Location
    Burleson, Texas
    Posts
    1,741
    If I understand correctly-you just had this installed, then I would have the installer seal the tape joints,duct connection and where the plenum is attached to the equipment.IMO that should part of the install...

  3. #3
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    If the tape they used is the metal foil tape with red or black printing on it, I wouldn't worry about painting mastic over it. Inspect it every few years to make sure none of it is coming loose, but it probably won't.

    Definatly seal up any and all duct and plenum connections that are not well sealed. Also seal around any pipe and wire penatrations into the furnace or air handler, and around drain connections.

    Even if they don't seem to be leaking air, I would recommend that you tape the seams around all the access panels on the indoor equipment. Especially on attic and crawl space units, it is amazing how dirty even a small air leak around a blower or coil access panel can cause the inside of the unit to get.
    If more government is the answer, then it's a really stupid question.

  4. #4
    Join Date
    Jun 2005
    Posts
    77
    So the mastic can be applied right over the tape??

  5. #5
    Join Date
    Feb 2005
    Location
    Alabama
    Posts
    534
    Yes, mastic directly over the tape, make sure to cover any seems that you think might be leaking. I mastic all of my jobs, makes the boss and homeowner happy.
    "If you can't fix it, don't break it."

  6. #6
    Join Date
    Jun 2005
    Posts
    77
    Is the mastic messy or does it pretty much stay where its put?? Mastic right over tie wraps, tape, duct board, anywhere there is a duct or plenum connection?

  7. #7
    Join Date
    Feb 2005
    Location
    Alabama
    Posts
    534
    Exactly right mike, mastic everything that you mentioned. Mastic is not messy, it's pretty thick but try not to get it on your clothes. If you do get some on yourself or your clothes, wash it off with warm water BEFORE it dries. Here's a good link if you want more information. http://www.rcdcorp.com/

    If you're wondering, I use the #6 mastic found in that website.
    "If you can't fix it, don't break it."

  8. #8
    Join Date
    Jun 2005
    Posts
    77
    Thank you. You have been a great help

    Can you help on my question about the Scroll Compressor and whether vacuuming the sytem pulls the oil out of the compressor?

  9. #9
    Join Date
    Feb 2005
    Location
    Alabama
    Posts
    534
    When you pull a vacuum on a system, both service valves should (must) be shut. You want to pull the vacuum on just the lineset and a evap coil. If you need to remove oil from a lineset, you need to purge with nitrogen. I.E., if you're converting a system from R22 to R410a and can't run new copper. That can be quite an involved process depending on how long the lineset is. Too much info?? LOL Simply put, pulling a vacuum on a system will not remove oil from the compressor.
    "If you can't fix it, don't break it."

  10. #10
    Join Date
    Jun 2005
    Posts
    77
    so the oil in the compressor is isolated and remains in the system during a vacuum to 500 micron??

    Vacuum doesnt remove any of the oil?


  11. #11
    Join Date
    Feb 2005
    Location
    Alabama
    Posts
    534
    Exactly right.
    "If you can't fix it, don't break it."

  12. #12
    Join Date
    Jun 2005
    Posts
    77
    I will be sure to let you know if the piston changeout, vacuum and recharge results in a quiet compressor. I have been told the copelands can take some abuse so hopefully a couple days running loud didnt do any real damage.

    thanks friend

  13. #13
    Join Date
    Feb 2005
    Location
    Alabama
    Posts
    534
    Very welcome. Make sure to use a charging chart for fixed metering (piston) type systems. That way you'll have it right.

    [Edited by duct dr on 06-08-2005 at 05:29 PM]
    "If you can't fix it, don't break it."

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