Silicone or special duct caulk????

[mc1984ss]

I got a few joints where I noticed quite a bit of air leaking past and just wanted to put a dab of caulk in the corners to seal them up. It looked like the HVAC guys used regular silicone but I see they sell a special ductwork caulk. Is it really special???? Should I use the "special" stuff or will plain ol' silicone be fine?

Thanks in advance!

 

[u2slow]

The HVAC guys I know call it 'mastic'. Comes in a small bucket. Grey goo. Has some fiber product of some kind in it to help build up and fill over gaps. I think you have found the caulking tube version of it there.

I used it to reseal the joints on the main plenum for the furnace/air-handler when I reno'ed the laundry room. Worked out nice.

 

[tab2]

https://www.carlislehvac.com/product.aspx?id=40

This is what I see on all our jobs. (Commercial work in MA.)

 

[fitter30]

https://www.amazon.com/dp/B0085UZBE2/?tag=atomicindus08-20
Brushes on $15 for gallon

 

[Jim greengo]

UL 181 tape looks better.

 

[tinmanwpk]

I would use the duct sealer. I've seen fiberglass reinforcing tape used where they embed it in a coat of mastic, tape, then mastic. After it cures if you want to "hide" it with UL tape for aesthetic purposes, then fine. The tape alone I am of the opinion will not last as long as the aforementioned application. However, if you want to only use one coat of mastic period you'll be fine.

 

[Jim greengo]

If you use the mastic atleast run masking tape on either side of line before you slop that stuff on.
Then peel the tape off after it starts to set up so you have a straight line.

 

[bonneyman]

It goes by several names, several companies make their own version. I use something called White Pookie.

Get it at the sheet metal supply house. Like 65-75% solids, UV resistant, adheres to just about anything, remains semi-flexible when dry so it "moves" with the ductwork..
Be forewarned - don't let it dry on clothes or hair. It's dang near impossible to get off without destroying the garment ...or your head.