Duct mastic vs silicone
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  1. #1
    Join Date
    Mar 2005
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    I'm getting ready to assemble some ductwork. Advice from an HVAC relative is to use silicone caulk to seal takeoff collars, duct joints, etc. Everything I read here references mastic/mesh and/or UL181 tape.
    What would best practice be? If mastic, is the stuff available at home centers good, or do I need to go to an hvac supply house?
    thanks!

  2. #2
    Join Date
    May 2004
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    Rapid City, SD
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    Well, let me be the 1st to say "you should have called a pro". Be prepared to hear that about a dozen more times.

    Ok, enough sarcasm... I'd go with mastic (aka pooky). Silicone is somewhat messy (at least when I put it on), some of it can really stink, and it's somewhat time consuming to put on.

    Mastic gets smeared on with a cheap paint brush, doesn't really smell and cleans up with water.

    About the only time I use caulking to seal duct is if it's going to be exposed in some fancy building (mostly commercial). If it's in a residential setup and exposed, I still pooky.

  3. #3
    Join Date
    Sep 2004
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    3,157
    What kind of Duct is your company installing on this job?

    The company I work for uses about 4 wraps of packageing tape
    on flex

  4. #4
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    Jan 2005
    Location
    Seattle
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    191

    sealers and there applications

    CT2.Your kiding right.Just yanking are pee pee maybe.Just joshing around with us RIGHT.....Packageing tape? Are you talking the clear stuff or the brown???

    jhcrowman. In regards to sealer applications.I use silicone on the furnace or air handler sets.For one and only reason.Aesthetics.Yes, Silicone can be messy.It will get every where if your not very carefull.But a clear silicone looks SOooo much nicer.alot more professional than a bunch of grey or white pasty looking stuff smeared all over.I did one time have(get this guys)a inspecter all most tag me for using silicone on the sheet metal.Why you say? Well in the galvinized sheet metals manufacturing companys specification sheet he had at the office.It said silicone will etch the galvinizing!!!!!. WELL we would'nt want that now.Well as it turned out he was a really nice guy.He was going to LET me slide just this one time.Anyway silicone on the furnace and air handlers and any exposed take offs.Mastic on all the ducting seams.Also the mastic you can buy at the big boxs of this world works just fine.
    41GASMAN




  5. #5
    Join Date
    Aug 2003
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    1,841
    You should have called a pro right

    I like silicone,mastic is very messy.

  6. #6
    Join Date
    Feb 2005
    Location
    Alabama
    Posts
    534
    On metal duct, silicone. On duct board, mastic.
    "If you can't fix it, don't break it."

  7. #7
    Join Date
    Oct 2004
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    1,722
    The only time I've used silicone is to seal the gaps where copper goes into the A/H. I've never used it to seal duct...but that's just my experience.

    [Edited by square2round on 03-10-2005 at 09:58 PM]
    Get back to work.

  8. #8
    Join Date
    Aug 2003
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    1,841
    Originally posted by square2round
    I've never used silicone for sealing. That's just my experience.

    So what do you use silicone,mastic or tape?

  9. #9
    Join Date
    Oct 2004
    Location
    PDX
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    Re: sealers and there applications

    Originally posted by 41gasman
    CT2.Your kiding right.Just yanking are pee pee maybe.Just joshing around with us RIGHT.....Packageing tape? Are you talking the clear stuff or the brown???




    I think that he is talking about that UL 181 listed Mylar tape that you use for the flex connections. It looks and feels just like packing tape, but it is black and has the UL181 listing on it.


    As far as Silicone is concerned, I HATE it when I have to changeout a furnace that has been siliconed....Bloody murder trying to scrape all that stuff out to get the unit free from the can....Arrgh..
    I actually use foam weatherstripping for the furnace connections, and for my sheetmetal joints, they are S and Drive connections with a layer of foil backed mastic tape on the seams, including my round WA pipe stuff... That mastic tape is the best, no mess no fuss (except for that blue liner tape on the mastic you gotta pick after you make the joint...
    They sell it at the box stores as well... Kinda expensive but well worth it.

    [Edited by oloenneker on 03-10-2005 at 10:03 PM]

  10. #10
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    Feb 2004
    Location
    southern illinois
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    have used aluminum type stuff before made by alcoa,...comes in a tube and when it sets up..........good-luck trying to get it apart.Blends in nice with the metal too.As far as preference,.....i don't really have none one way or the other.Both work just fine......

  11. #11
    Join Date
    Oct 2004
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    1,722
    Originally posted by framehvac
    Originally posted by square2round
    I've never used silicone for sealing. That's just my experience.

    So what do you use silicone,mastic or tape?
    I use tape and mastic. It may be overkill, but I feel better.
    Get back to work.

  12. #12
    Join Date
    Aug 2003
    Posts
    1,841
    Originally posted by square2round
    Originally posted by framehvac
    Originally posted by square2round
    I've never used silicone for sealing. That's just my experience.

    So what do you use silicone,mastic or tape?
    I use tape and mastic. It may be overkill, but I feel better.

    I use to do that to but then I tried silicone,I love it.

  13. #13
    Join Date
    Nov 2004
    Location
    Cincinnati
    Posts
    7

    Exclamation silicone

    Has anyone read Bryant's white paper on evaporator coil
    failures ? one of the main culprits is acetic acid.
    Go to the site and read up
    thanx

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