Replies

1. 
   MarkH | Mar 26, 2011 06:04pm | #1

   A mastic designed for sealing ducts is generally used.  This website has an example of the products.  http://www.rcdmastics.com/

1. 
   Hal | Mar 26, 2011 09:52pm | #4

   A mastic designed for sealing

   Mark,

   Thanks for the link.  I saw this product being used on some youtube videos, but unfortunately I cannot find it in any of the big box stores Home Depot, Rona, etc.) where I live, Ottawa.  I haven't yet checked out any HVAC outlets.  I was just wondering if a caulking product would be safe to use.

   David

2. 
   DanH | Mar 26, 2011 09:11pm | #2

   As stated, there's a "duct

   As stated, there's a "duct mastic" designed for sealing ducts, and probably the best choice.  For residential use you could use silicone caulk and it likely would work fine (be sure to wipe down the surface first with an alcohol-dampened rag to remove dust and oils).  However, in commercial construction the BI would probably have a conniption if you used silicone, as it's not fire-rated.

   For larger holes there's another option which is a sort of non-hardening putty that the HVAC guys use.  Not sure what it's called, but it's similar in consistency to plumber's putty or "duct seal" (electrician's putty).

   On Google I see both HD and Lowes advertising duct mastic.

3. 
   DanH | Mar 26, 2011 09:15pm | #3

   FWIW, I happened across this PDF which seems to contain some useful info:  http://www.energydesignedhomes.com/Papers/DuctSealing.pdf

4. 
   xxPaulCPxx | Mar 27, 2011 12:29am | #5

   HD should have it by the tube and by the bucket in the HVAC dept, near the metal tubes and fittings for HVAC.  It's a water based product.

5. 
   rdesigns | Mar 28, 2011 11:44am | #6

   I know of many, many HVAC duct systems that have used silicone for air sealing, and I've never heard of any trouble or complaints.

   To me, the drawback on silicone is the difficulty of reaching tight places with a caulking gun.

   The mastic that was suggested is much easier to get into tight places. You use a brush or putty knife for most places, and a latex-gloved hand to smear it on in other places.

6. 
   Tim | Mar 28, 2011 05:22pm | #7

   Safe and practical

   Any standard silicone or RTV type of sealant is safe to use on the ducts. As some others have pointed out, mastic is a more practical (read: cheaper) material, but it can be difficult to locate in some areas. I worked at an HVAC supply house that didn't even carry it. I only see mastic used (in this part of the world, at least) in commercial ducting, and then not consistently.

   I like the heavy foil tape to seal take-offs and transistions and some crimped connections, depending on the location. What's wrong with the foil duct tape you were using? You obviously have access to it.

1. 
   Hal | Mar 28, 2011 08:55pm | #8

   Duct Tape

   Nothing wrong with the duct tape.  I just had a few joints/holes to patch that were hard to get at and cover with the tape.

   I've heard of the mastic but am having difficulty locating it.

   BTW Tim, what do  you mean by 'RTV ' type sealant?

   Thanks

1. 
   DanH | Mar 28, 2011 11:49pm | #9

   Nothing wrong with the duct tape.

   So long as it's duct tape (foil) and not duck tape (cloth).  The latter never was intended for sealing ducts.

1. 
   Clewless1 | Apr 10, 2011 06:26pm | #11

   I think originally, grey duct tape WAS intended to be used for ducts. Until they found out that it dried out and didn't do much good.

    

   Now days with options available ... my motto is 'duct tape ... good for everything ... but sealing ducts.'

   Did you see the duct tape episode of Myth Busters? Pretty interesting. I also saw a story on line where a bear tore a small plane to shreads trying to get at some food in a cooler. The guy duct taped the fuselage back together and flew it back home so he could repair it later. Wow!

1. 
   DanH | Apr 10, 2011 07:43pm | #12

   No, the original gray tape was invented for the military, for sealing ammunition cans and the like.  It was called "duck" tape because it was made from duck cloth.  Never was intended for sealing ducts.

   http://en.wikipedia.org/wiki/Duct_tape

2. 
   Clewless1 | Apr 11, 2011 08:06am | #13

   Learn something every day. I guess it was earlier commonly used to sea ducts before the advent of mastic and other tapes.

   I stand corrected. Thanks for the historical tidbit Dan. You da man!

2. 
   Tim | Apr 01, 2011 03:54pm | #10

   RTV means "room temperature

   RTV means "room temperature vulcanizing". Rubberized sealants were refered to as RTV as a generic term. MOL, what caulk and silicone used to be refered to.

   Once upon a time, you couldn't buy a tube of goo that you could squirt on to a crack or seam that just "set up" all on its own, such as is the norm today.