# Mastic vs foil tape



## Dak Man (Jul 4, 2015)

Depends on how it's applied. And where. Code changed a few years ago down here in south Texas to either one or the other being if foil tape it has to be UL listed tape versus cheap tape covered in mastic. Inspectors like and need to see the ul listed print on tape. But we always use both still just in different areas. Tape a collar to a plenum and once duct is installed mastic seal duct to plenum around collar.

Ideally both but Mastik can get in crevices and fill all voids. 

If you're asking what is better as in if you had to choose I'd say mastic. remember it takes days for it to dry but once it does you're golden.


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## Bob Sanders (Nov 10, 2013)

The tape is easier. Less mess and you can do joints as you're putting the ducts together. There are some joints easier done on the ground rather than after it's up and that tape acts as a filler AND a connector.

I had the joy of redoing all of my ductwork this Summer and with all the tight spaces I was working in, there was no way in the world any mastic compound would have done the job.


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## drew53813 (Jun 25, 2014)

Can you recommend a good tape to use?


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## nap (Dec 4, 2007)

First I don't think either is intended as a repair themselves although each can be used as part of a repair. 

What I see in the commercial installations is;

Mastic is used to seal steel (hard) duct. Foil Tape is used to seal duct board and insulation that is foil backed. I have never seen a successful use of foil tape on steel duct. It does t conform to odd shapes and it often does not stick well enough. While mastic over tape would be ok I don't see the purpose. 

Each is designed for specific uses. Use them each as they were designed for and you will have fewer problems down the road 

As you can see I disagree with bob sanders. While I respect his opinion I simply do not agree. 

And mastic, while often messy, can be installed easier than tape in s confined space. If you get dirt on the tape (as an example) as you try to wrap it around a duct that is in a tight place, it won't stick. Even if you cannot get a brush in to spread the mastic you can use things like a Terry cloth car wash mitt to smear it on quite well.


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## drew53813 (Jun 25, 2014)

I have been reading that mastic is a far superior method for sealing duct work than foil tape


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## Bob Sanders (Nov 10, 2013)

nap said:


> And mastic, while often messy, can be installed easier than tape in s confined space. If you get dirt on the tape (as an example) as you try to wrap it around a duct that is in a tight place, it won't stick. Even if you cannot get a brush in to spread the mastic you can use things like a Terry cloth car wash mitt to smear it on quite well.


Well the object is not necessarily to smear it on but rather to seal a particular gap. Can't do that if you can't see it.... or get at it directly. I CAN seal a gap with tape without seeing it. I can (and have) thread a piece of tape through a 1/2" gap between the duct and the floor above, and floor joists on the sides and end up with a positive seal. There is no way in the world I could do that with any confidence with mastic and a rag taped to the end of my fingers.

You're free to disagree of course but at the end of the day with tape (unlike mastic compounds)... I know I have sealed it all


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## Bob Sanders (Nov 10, 2013)

drew53813 said:


> Can you recommend a good tape to use?


I used this stuff... only because I had a ton of it laying around;

http://www.ebay.com/itm/3M-TM-Aluminum-Foil-Tape-425-Silver-US-2-in-x-60-yd-4-6-mil-/141038536999

But there are lots of different qualities and thicknesses out there.. I would stay away from the cheap stuff though. It's thinner than tin foil.


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## nap (Dec 4, 2007)

Bob Sanders said:


> Well the object is not necessarily to smear it on but rather to seal a particular gap. Can't do that if you can't see it.... or get at it directly. I CAN seal a gap with tape without seeing it. I can (and have) thread a piece of tape through a 1/2" gap between the duct and the floor above, and floor joists on the sides and end up with a positive seal. There is no way in the world I could do that with any confidence with mastic and a rag taped to the end of my fingers.
> 
> You're free to disagree of course but at the end of the day with tape (unlike mastic compounds)... I know I have sealed it all


it's an "if the normally recommended method is not possible, use what you can to effect the application". Mastic is simply smeared on with a paint brush. If one cannot utilize a brush, a gloved hand provides a decent alternative and can get where a brush cannot be used often times. 

as to being able to seal a gap with tape without needing to see it; you can't see if your tape is properly adhered if you cannot see it. 




> I can (and have) thread a piece of tape through a 1/2" gap between the duct and the floor above, and floor joists on the sides and end up with a positive seal.


huh? First, there should never be a 1/2" gap you need to seal. The installation needs to be corrected first then the remaining air leaks sealed. Neither mastic nor tape is intended to seal large gaps like that.


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## Bob Sanders (Nov 10, 2013)

nap said:


> as to being able to seal a gap with tape without needing to see it; you can't see if your tape is properly adhered if you cannot see it.


That's just it... with tape you don't need to see it. You can feel it.




> huh? First, there should never be a 1/2" gap you need to seal. The installation needs to be corrected first then the remaining air leaks sealed. Neither mastic nor tape is intended to seal large gaps like that.


I think you misunderstand.... not a 1/2 inch gap in the duct work. If you 1/2 inch gaps in your duct work then you aren't doing something right.

A 1/2 inch gap between the duct work and various structures of the house.


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## nap (Dec 4, 2007)

> Bob Sanders;2304161]That's just it... with tape you don't need to see it. You can feel it.


you can feel what? I have been fooled terribly by feeling something and it not being what I thought it was. We don't want to get into explanations of what that is referring to








> I think you misunderstand.... not a 1/2 inch gap in the duct work. If you 1/2 inch gaps in your duct work then you aren't doing something right.


that was my point so if you are not trying to seal a 1/2" gap then yes, apparently I am not understanding what you mean. 



> A 1/2 inch gap BETWEEN the duct work and various structures of the house.


Oh, so something I can use a rag on a stick to shove mastic into to seal the duct. Gotcha:wink:

so here we are again, diametrically opposed to the other's point. While I understand your points, I simply do not agree...and that's my right, dang it.
I simply prefer mastic for any place mastic is called for. 


I'm starting to think you are visiting the left Twix factory while I'm at the right Twix factory



and if that doesn't make any sense, either ignore it or ask and I will explain. It comes from a commercial for Twix candy bars.


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## Bob Sanders (Nov 10, 2013)

nap said:


> that was my point so if you are not trying to seal a 1/2" gap then yes, apparently I am not understanding what you mean.


Oh dear. No one said anything about sealing 1/2 inch gaps. When you hang your duct work in tight spaces often you are left with tight spaces *AROUND* your duct work where you can't get brushes and rags and eyes... etc. For example you are left with a 1/2 inch gap *BETWEEN* your duct work and other structures of the house.

With tape I can assemble what I need to, and can on the ground and hang it as a whole piece, or thread tape into tight spaces after the fact.



> you can feel what? I have been fooled terribly by feeling something and it not being what I thought it was. We don't want to get into explanations of what that is referring to


I just redid all the duct work in my house and wasn't fooled once. Dumb luck? Maybe... or just maybe I knew what I was feeling for.


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## nap (Dec 4, 2007)

> Bob Sanders;2304273]Oh dear. No one said anything about sealing 1/2 inch gaps.


 we were talking about sealing duct and you mentioned a 1/2" gap. What can I say Bob?




> When you hang your duct work in tight spaces often you are left with tight spaces *AROUND* your duct work where you can't get brushes and rags and eyes... etc. For example you are left with a 1/2 inch gap *BETWEEN* your duct work and other structures of the house.


 I know what you mean not but I have a problem: my hands don't fit in a 1/2" gap to feel the tape. Now what?





> With tape I can assemble what I need to, and can on the ground and hang it as a whole piece, or thread tape into tight spaces after the fact.


and with mastic I can grab a car wash glove and go to town. 






> I just redid all the duct work in my house and wasn't fooled once. Dumb luck? Maybe... or just maybe I knew what I was feeling for.


I have these big callouses on my hands. Makes it tough to feel fine detail. 



seriously bob, hopefully you understand I have been kidding around a bit. Basically, you stay with your tape and I'll stick with mastic (get it, stick, like it's sticky). 

so what material is your duct made of? if metal, what kind of joints?

I'm used to seeing bolt together duct or duct with "drives" where tape would not be practical or sensible (in my opinion just in case that is what you have:thumbup and mastic is the only answer.

even with a slip fit duct you have the seams that, to me, would be much easier to seal with mastic than tape. 

but to each their own.


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## Bob Sanders (Nov 10, 2013)

nap said:


> so what material is your duct made of? if metal, what kind of joints?
> 
> I'm used to seeing bolt together duct or duct with "drives" where tape would not be practical or sensible (in my opinion just in case that is what you have:thumbup and mastic is the only answer.
> 
> ...


All metal except for two returns which are lined floor joists. Mostly slip joints. Don't like using screws. They pierce into the duct work and act as hangers for dust and dog hair. With tape there is no need for that.


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## Dak Man (Jul 4, 2015)

Bob, did you invent foil tape? :thumbup:

I've been in the biz for 16 years now, both commercial and mainly residential. Mastik is the final say so of all things air sealing. Try sealing a chase in an attic with foil tape. :no:

Mastik is 100 times more effective especially when it comes to condensation, dirt, heat, cold, mice, goats, giraffes, lions and tigers and bears too. 

Bob, I can make your system more efficient simply by using mastic. Check the heat transfer through foil tape. Mechanical heat is not a factor with mastic. 

Anywho...


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## nap (Dec 4, 2007)

> Mastik is 100 times more effective especially when it comes to condensation, dirt, heat, cold, mice, goats, giraffes, lions and tigers and bears too.


Oh my!!!


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## Bob Sanders (Nov 10, 2013)

Dak Man said:


> Try sealing a chase in an attic with foil tape.


I tried... and succeeded.



> Battle of the Tape: Duct Mastic vs. Foil Tape


http://murraylampert.com/battle-of-the-tape


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## Dak Man (Jul 4, 2015)

oh Bob, Bob, Bob.. 

sealing a chase in an attic is to prevent heat transfer, not to simply cover a hole.


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## Bob Sanders (Nov 10, 2013)

Dak Man said:


> oh Bob, Bob, Bob..
> 
> sealing a chase in an attic is to prevent heat transfer, not to simply cover a hole.


You use proper insulation for that. At least I did


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## Dak Man (Jul 4, 2015)

got pics?


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## Bob Sanders (Nov 10, 2013)

Dak Man said:


> got pics?


Of the attic?
No.. and I have no plans on climbing up there again.


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## user_12345a (Nov 23, 2014)

> sealing a chase in an attic is to prevent heat transfer, not to simply cover a hole


For general attic air sealing around lights/chases, spray foam is the best.

For sealing ducts in an attic mastic sounds better. Tape can fail in intense heat and cold after a while; as someone who has never worked in an attic, I can say, once you've gone up there to seal ducts, you'll never want to do it again. Sealing ducts in a basement ceiling in tight spaces is enough of a pain, i can imagine doing it in an attic with no floor and dusty/itchy insulation. Do something permanent.


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## Dak Man (Jul 4, 2015)

Bob Sanders said:


> You use proper insulation for that. At least I did


Bob, daily I charge $329 to seal single attic chases (20 minutes of work using 2" ductboard and mastic) and $600 to mastic air lock complete systems., about 20 minutes as well. Insulation and energy efficiency are why I now average 7k a week. I sell systems, but I won't do so unless I know the system is doing what is expected of it and that means only conditioning living space so in other words along with systems I perform blower door whole house energy efficiency tests to determine and correct not the ac system, the dwelling. Once that is as best as I can get it I concentrate on system efficiency.

Return airs, air lock, heat loads. Without those you don't get a system from me. 

I know insulation, my friend. I know it so well I can take your house and cut your bills in half. And I won't use any foil tape. 

I appreciate your enthusiasm, I will say this for foil tape, you must know how to apply it to get the most from it. It seems as if you do know it.

Okay, twas fun. :thumbsup:


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## Dak Man (Jul 4, 2015)

side note: in 33 years in business my boss told me no has made 10k in one week. Two months into employment I brought home 11k, five days work.

people pay big for efficiency down here, you just gotta know how to get there. :yes:


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## ProGreen (Oct 2, 2014)

I applied the gray mastic with a paint brush to all of the solid duct joints I came across last summer. I had removed all the ducts old exterior insulation for inspection first. I am sorry I didn't use the thicker white mastic with gloves (hadn't heard of it and may still do it. I made sure the duct system was inspected by our HVAC man first for any onerous duct breaks etc., although admit to fixing one dislodged with proper duct suspension to tighten joints, then wrapping it with water resistent foil tape.

I'd say go for it if you have the inclination and time. I'd recommend the heavier white compound. I'm a homeowner with a large metal duct system that extends from return/supply furnace into two crawls. Good luck.


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## beenthere (Oct 11, 2008)

drew53813 said:


> As the title says: mastic vs foil tape for residential duct work repair


Mastic is a more permanent method. Foil tape a less messy way.

If you want a more permanent way, with less mess, use a mastic tape, like Hardcast tape.

http://www.ebay.com/itm/like/321032199173?lpid=82&chn=ps


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## supers05 (May 23, 2015)

Our engineers here (and therefore inspectors) demand we tape, then use duct sealant. All new engineered commercial installs are like this now for us. I suppose yet another view point of the thread. 

Cheers!


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