Mastication

[soshin]

I am in the middle of a residential construction project where they have just started putting in the HVAC system. I am talking to the installer about how important it is that the system be sealed well, that I want a blower door test once everything is finished, etc.

The topic comes around to how they are sealing the seams, particularly on the hardpipe and around the joints. He told me that the joints were screwed then taped using a UL 557 product. He said this worked well and that they try not to use mastic much because mastic takes too long to dry and that the insulation guys just end up pulling it off anyway when they put their insulation on. I went down in the crawlspace and sure enough all the seams that I could see were sealed with this tape. I would like to get your opinion of whether screwing then taping is enough or if I should insist on mastic. Thanks.

[cem-bsee]

depends upon the product & applyer --

my original ducts were sealed in 1974 with duct tape, which I can not now remove -- but, just the joints of the supply ducts. said tape has not fallen off anywhere.

however, no seams nor plennum holes were sealed. I have since applyed mastic with a putty knife.

so, why not schedule the insulators 3- 5 days later?

does the tape have a metal backing? I used some to seal the insulation around pipes in the attic -- seems to be quite sticky -- but I will not be here 25y to judge --

if rest of job is ok, then that will be ok.

what about the plennum seams & holes? were the cracks around the register boots caulked -- between the boot & ceiling | floor ?

one can do a duct leakage test --

[albowrx]

What is this "Insulators" talk? The installer is suppossed to do that. Screws and 557 tape is good enough. I guess if you wanna be on the bad side of the installer you can opt for mastic, just dont expect a nice answer.

[41gasman]

soshin.Useing duct tape is not OK on a new system anymore.557 is just ducttape of a resonable quality.PLEASE PLEASE PLEASE do a "search" on sealing ducting and proper insulation.There has been a lot of threads on this subject.You just got to.you would not believe the differents it make to the performance and efficiency of your brand new system.As far as getting the mastic pulled off when the insulaters do their thing.Thats a bunch of toe jam.I seal all joints and the seams on all the hard pipe.Jump on the search feature here.Stay up burning that midnight oil.You have a lot of inportant things to learn and have done.Good luck if we can help,ask away.You need to make sure they do a good quality job on your install.But first you need to know what a good install consists of!
41GASMAN



[Edited by 41gasman on 03-10-2005 at 10:10 PM]

[oloenneker]

There are Mastic tapes avaialble that contain metal backing and mastic all in one tape. This stuff does last a ling time so there is nothing to worry about there. Plus the mastic is mess and does not look good and takes forever to apply. Not sensible in the slash and bang rates that new construction bid are brought down to these days..

[AllTemp]

Originally posted by soshin
I am in the middle of a residential construction project where they have just started putting in the HVAC system. I am talking to the installer about how important it is that the system be sealed well, that I want a blower door test once everything is finished, etc.

The topic comes around to how they are sealing the seams, particularly on the hardpipe and around the joints. He told me that the joints were screwed then taped using a UL 557 product.

If I am not mistaken 557 has a UL Listing but has a warnign Not A To Use On Sheet Metal ...

UL 181B-FX listed product - The Underwriters Laboratories, Inc. for closure systems for use with flexible air ducts and air closures. Possesses excellent shear properties. Superior quality, performance, and tensile strength. Shows excellent resistance to mold growth, humidity, flame spread, smoke generation, and the effects of high temperatures.



[Edited by AllTemp on 03-10-2005 at 11:21 PM]

[framehvac]

Originally posted by albowrx
What is this "Insulators" talk? The installer is suppossed to do that. Screws and 557 tape is good enough. I guess if you wanna be on the bad side of the installer you can opt for mastic, just dont expect a nice answer.

& plan to pay more for it.

[41gasman]

framehvac.
Plan to pay more for what?Mastic on all galvinized to galvinized pipe or fitting is code here.
41GASMAN

[BamaCracker]

"Mastication" is the act of chewing.

Just thought you would want to know. . . . .

[wormy]

In all fairness...
you should have discussed the installation practices with the contractor doing the hvac work before agreeing to have them do the work.

i.e.
contractor #1 gives quote... its real high...
contractor #2 gives quote... its real low...

you think you get the same quality work
So you choose #2

however, there are differences in the
quality/installation practices....
contractor #1 goes out of his way to do fine quality work
contractor #2 puts in flex pipe, does not balance air flow, etc

Once job is halfway done.. you become more educated as
to 'proper installation practices'.... you want
contractor #2 to do the same quality work as contractor #1
but you've already agreed to do the job, and more than
likely don't have a written agreement as to the quality
and standards of the work to be done.

---------------------------------------------


Its been a long time since I've been to this board.
Too bad it was with a sour post.
I hate to hurt anyones feelings or anything.

[41gasman]

Feelings......yea you hurt it.Damm nowmy feeling is gone.And it was the last one I had too!
41GASMAN

[robertee]

I'm one of the DIYs on the list and have gained a lot of knowlege here. I've been sealing all my joints with mastic and silicone. I went to several wholesalers and they don't even sell mastic. So you know the quality of work done in this area. I bought mine from Home Depot, expensive. The boots and elbos have so many joints with air leaks they have to be sealed. I even sealed the long joint in the round pipe. I want my system to be air tight. It is time consuming to use mastic but it comes in a caulking tube, more expensive at HD. I had one contractor tell me it won't hurt anything if conditioned air leaks under the house. I don't see him on this talk list.

[wormy]

I had one contractor tell me it won't hurt anything if conditioned air leaks under the house

Now thats funny.


Think of your house as a 2 litter plastic Coke Bottle.
Put your mouth to it and start breathing.
You are in essense a central air unit.
Your unit sucks the air out of the bottle and blows the same amount back in.
Now suck in a good bit of air, blow most of it back in and a little bit outside the bottle to similate a supply air leak.
It wont take long for the bottle to start collapsing because its running out of air.
Poke holes in the bottle to simulate air leaks in the house. i.e. PUll down staircases, light fixtures such as recessed lighting, recepticles along the outside walls.
Now all the air you blow outside the bottle gets replaced by the 'unconditioned'/unfiltered air outside the bottle.

In short... The air you blow under your house gets sucked back in from your attic. How would you like to suck in 120degree air into your house in the summer?

[41gasman]

robertee. I commend you for your efforts.It is a lot of work! But you can expect a lot more comfort and savings for you efforts.We have to seal with mastic all joint and seams per code.But what cracks me up is that you don't have to seal the elbow gores or the little holes in the boots and fittings(wys ext).But what I find most humorous is that you don't have to seal between the boots and the floor or ceiling.I use a skill saw when I cut out the floors because I can get a lot nicer fit.Reciprocating saws are a excellent
tool BUT are not known for there precision.You should see some of the kinda square kinda 4"x10" or 12" 14"that get cut in on the new constrution around here.The amount of leakage here is quit large.
Have a good day you guys.
41GASMAN

[golf junkie]

Originally posted by wormy

I had one contractor tell me it won't hurt anything if conditioned air leaks under the house

That seems to be the prevailing attitude of contractors in this area too. Commercial jobs all get mastic....it's required in the job spec. But for residential contractors just don't want to do it and maintain that it's not necessary.

[AllTemp]

Originally posted by golf junkie

Originally posted by wormy

I had one contractor tell me it won't hurt anything if conditioned air leaks under the house

That seems to be the prevailing attitude of contractors in this area too. Commercial jobs all get mastic....it's required in the job spec. But for residential contractors just don't want to do it and maintain that it's not necessary.

Here in California effective this Oct 2005 all residential as well as commerical HVAC project require a duct test be performed by an outside independent contractor prior to passing inspection.

If you change outdoor system only, duct test is still required...

I'm sure everyone must know also that it will also be mandated that the indoor/outdoor units be matched not sure of that date.

I give a plus to California they have always been one step ahead the rest of the country with thier energy conservation.

This will help alot on situations such as the one in this post...

[corny]

California is ahead of the rest of the country in trumping up new ways to increase fees and taxes and get business for shady contractors.

What are they going to do about a house with a leaking takeoff on a duct system that is completely framed in and unaccessable..........yep...they will require the homeowner to rip their house apart and then let some fly by night buddy of the independant testing contractor come in and slap on a piece of duct tape that will undoubtedly fall off within a year........thats how california works...its a lot like the federal government.

[bluetooth751]

Originally posted by AllTemp

Originally posted by golf junkie

Originally posted by wormy

I had one contractor tell me it won't hurt anything if conditioned air leaks under the house

That seems to be the prevailing attitude of contractors in this area too. Commercial jobs all get mastic....it's required in the job spec. But for residential contractors just don't want to do it and maintain that it's not necessary.

Here in California effective this Oct 2005 all residential as well as commerical HVAC project require a duct test be performed by an outside independent contractor prior to passing inspection.

If you change outdoor system only, duct test is still required...

I'm sure everyone must know also that it will also be mandated that the indoor/outdoor units be matched not sure of that date.

I give a plus to California they have always been one step ahead the rest of the country with thier energy conservation.

This will help alot on situations such as the one in this post...

I have to say that is nice, and so is California.

[Steve Wiggins]

Why Why Why does everyone stress out about the duct joints leaking? The major leaks are where the ducts join the plenum and the equipment door panels, and around the supply ducts where they penetrate the ceiling/floor.

I do not advocate putting a system together that can't be taken back apart. maybe the 557 is not the right tape but mastic is a mistake IMO. Code writers have went totally berzerk with this and now require it on the vapor barrier too which is completely ridiculous.

http://www.achrnews.com/CDA/ArticleI...nalNews_Item/1,6084,128736-South,00.html






[Edited by Steve Wiggins on 03-13-2005 at 10:17 AM]

[wormy]

I don't have any trouble taking apart duct that's got
mastic on it. (then again... the only time I ever have to
take it apart again is if the homeowner remodels their
home or I have to replace the hvac equipment.. no biggy
either way) We use a brand called Air Seal... it works
real good and the ducts come back apart without a ton of
effort. I have seen some mastic that sets up like a hard
epoxy coating or something, maybe thats the kind you've
seen.

I am very picky when it comes to air leaks in duct work.
As I said earlier, the house sucks in the same amount of
air your duct system leaks out. This not only leads to
comfort issues (ask all the people around here that
condemn heat pumps due to air leaks in their duct system),
it also leads to mold/mildew/growth problems.
ALL air leaks are important.

I'm pretty sure someone is going to wonder about the 'new'
addage... "They make houses so much airtite these days"
In my opinion, the 'airtite' homes really need economizers
put on the equipment to allow for fresh air to be brought
into the house in a controlled / filtered manner.
Albeit, selling a customer on this is kinda tough though...
i.e. Customer spends thousands of dollars to get his house
energy effecient... ala airtight
HVAC contractor comes along and says...
since you have such an airtight house, we need to install
a fresh air intake on your system to bring in outside air.

One of my duties at work is to do Heat Pump setup and
preinspection. (trying to give short version of it)
I had one very recent that measured 15% UNDER rated
capacity. Not only did it reduce the unit from a 3.5 ton
to a 3 ton.... it also introduced more moisture into the
house, more dirt into the duct system, and so on)
It had about 30ft of duct with the slips and drives not
sealed.
I had our installers seal it up with Air Seal.
Now I have Full Capacity.

Just by looking at the duct, it didn't look like it was
leaking much. Especially being a tad bit oversized and
the static pressure being on the low side.
So the duct wasn't 'sucking that hard' to pull the air in.
The air temp under the house was only about 50degree's too.

HEre's another reason to seal your supply ducts...
IN the summer, those air leaks are going to be blowing
cold air into the insulation. The insulation has a
foilback covering that helps prevent the air from leaking
out there, so the air migrates to the stapled seams and
ends where the insulation buts up to one another.
Surface temp of insulation drops below dew point of
environment its put in.
Surface of duct wrap starts sweating.
After an extended period of time, the moisture barrier
(foil back) starts to become saturated. Then the
insulation acts as a sponge absorbing the water. Then the
insulation gets all soggy. Then it stops resisting heat
transfer. and then and then and then muahahahahha
Plumber crawls under house and comes out telling homeowner
about the duct wrap is completely filled with water and
falling off the pipes.
Homeowner gets mad at hvac contractor cuz they spent
thousands of dollars to get the job done and now its
falling apart.