How long to let mastic on collar dry?

Problems related to residential installations.

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How long to let mastic on collar dry?

Post by RunningLow » Sat Jul 18, 2015 5:03 pm

In 95 F deg attic (probably 105 now) @ 50 - 60% humidity, how long to let the "1st coat" of mastic dry, before installing flex duct?
It's 8" collar, 8" R-8 flex.

Instructions say "allow to dry 48 hours before ** pressure testing ** " (I believe).
Nothing mentioned about at what temp, or humidity, etc.

Don't want to risk the mastic not being bonded as strong as needs to be, before stretching / pushing / messing with the new duct.
Seems like a long time to wait in hot weather, if people had no AC?

Put a new start collar, on rigid duct board plenum this morning.
All surfaces cleaned 1st w/ alcohol.

Put one med. layer mastic - thick enough to hide (most) the corrugated flange & enough to hide the silver duct.
Then brushed over mesh tape enough to cover it with mastic.

So, not a very thick layer mastic. Will add 2nd coat later.

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- How long to let mastic on collar dry?

Post by Freon » Sun Jul 19, 2015 10:21 am

Test it in 24 hours. If it's hard and dry you should be good to go for a second application.

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