Get tips on how to seal duct joints with mastic. Learn why duct tape doesn't work on ducts.
LESLIE: Our next caller takes us to Tennessee where Tony is looking to do some artwork on the tin ductwork.
Are you thinking of putting like cape paintings or you just want to paint them a solid color? What are you looking to do, Tony?
TONY: Ducks. I want to paint ducks on there. (Leslie laughs)
TOM: (laughing) Ducks on ductwork.
TONY: Ducks on the ductwork.
TOM: (laughs) That’s great.
LESLIE: Well, you’re going to need a yellow paint.
TONY: I noticed at that restaurant that they were visible where they were remodeling .
TONY: They had painted like a gray paint over the ductwork and joints instead of using duct tape. And every experience I ever had with duct tape was bad.
TONY: I’ve never had a good experience with it.
LESLIE: Well, because it’s not made for ducts.
TONY: Amen. It doesn’t even work on the foam that you put around hot water (inaudible).
LESLIE: It makes excellent wallets, though.
TONY: (laughs) There is a website somewhere that tells you all the different uses.
TOM: Yeah, the duct tape guys. (chuckles)
TONY: I don’t believe that stuff is very good with the weather.
LESLIE: No, you can use duct tape though, they say, to get rid of plantar warts. They say there’s something in the tape glue that gets rid of them. (Tom chuckles) How weird is that?
TONY: (laughs) That’s something else.
TOM: Hey, my friends the duct tape guys wrote like four books on – or maybe even five books on uses for duct tape. But you know, duct tape is great for everything except for what you said, Tony; it’s not good for ducts. And by the way, that silver stuff that you saw around the joints, that wasn’t tape; that was probably mastic. And good-quality HVAC contractors use a mastic to seal the joints now – in fact, the new energy codes require it – because that’s where you get a lot of leakage.
Now there is one type of tape – not to get too far off your question about paint – that does work and it’s called UL 181  tape. It’s like a silver-faced tape that has a special glue on it; and of course it’s more expensive than duct tape but it works. It sticks on there once and for all and it doesn’t come off. So there is a type of tape that will work to seal a duct joint but it’s not duct tape.
TONY: Alright. But that mastic, do you know what it’s called or anything about that?
TOM: Yeah, it’s just called mastic and if you go to any HVA supply house, they have it there. It’s sold in tubs – you know, in one-gallon or five-gallon buckets. And it does a really good job of sealing in the joints.
TONY: That’s good. That’s what I need. I also understand – you were talking to somebody about the moisture the other day; in the insulation?
TONY: Building up above their ceiling?
TONY: And that’s one of the things that you didn’t mention was it’s leaking out of the – oh, like in the air conditioning season.
TONY: Cool air coming back through the duct into the intake will sometimes – there or in the exhaust part going out to the house – will leak through those joints into that insulation. If there’s any punctures, boy, you get the moisture in a hurry. (chuckles)
TOM: Yeah, you’re absolutely right, Tony, because that actually happened to me as well. This summer was just so humid, we had a leak over my son’s bedroom which is right near where the air handler is. And at first I thought it was the overflow pan for the condensate but it wasn’t. It was actually condensation off the ductwork just because it was so unusually humid this particular year. And so, clearly, that can happen in extreme circumstances and that’s why it’s important to have your ducts all in a row and as tight as possible. (Leslie chuckles)
TONY: Yeah. Gosh, your ducts in a row. Did you add insulation  to yours?
TOM: Yes. We re-wrapped it with additional insulation as soon as it dried out and then resealed the joints and didn’t have a problem after that.
TONY: Oh, that’s what I’m doing right now is waiting for mine to dry out. (chuckles) Now that we’re in the heating season, it’ll dry out.
TOM: Very quickly.
TONY: Yeah, I’ll have to cut out that area around the joints, I think, and put that mastic on and then some of that narrow (ph) insulation in there and then put another blanket over the top of it.
TOM: Well, it’s money well spent, Tony, because a lot of energy is lost through leaky ductwork and if you seal them up, you’re going to be saving money and that’s more important than ever this heating season.
TONY: Well, I sure do appreciate that, y’all.
TOM: You’re very welcome. Thanks so much for calling us at 888-MONEY-PIT, 888-666-3974.