Mastic # 7 Metal Duct


  #1  
Old 11-20-22, 05:36 AM
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Mastic # 7 Metal Duct

Hello,

I am replacing the flex ducts on my house with metal pipes and was wondering if you can temporarily mount everything in place and then applying Mastic while the heat is running.
 
  #2  
Old 11-20-22, 06:51 AM
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Any air leaks will just push through the wet mastic, defeating the purpose. Either wait until you can shut off the fan long enough to apply the mastic and let it dry, or seal with foil (not duct) tape instead of mastic. If you seal with tape first, you could apply mastic with the system running if you want, but if you do a good job with the foil, you really don't need the mastic.
 
  #3  
Old 11-20-22, 06:57 AM
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Sorry, I forgot to mention that I am applying 3M foil tape before Mastic.
So, you would say that is it safe to use Mastic over the foil tape when the HVAC is running.
 
  #4  
Old 11-20-22, 04:37 PM
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Typically, you'd use either foil tape OR mastic. There's really no need to use both.
 
rndiy voted this post useful.
 

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