good quality foil tape.

When putting together a ductboard system, you have to understand that there is a male end and a female end to each 4ft section. Once i cut the board to the size i need, its folded into a square that has a flap that runs down the length of the board. This flap is folded over to the next side of the board, stapled all the way down, then taped with silver U.L. listed tape... usually 3" tape.

When connecting the 4ft trunks together, the male end of one trunk fits into the female end of the other trunk. Flaps are then folded up, stapled, and tripled taped with the same U.L.listed silver tape.



Here is the double tape...

and the final triple layer.

We will then cover all the silver tape with "Pookie" or a air seal that is alot like plaster of paris. I do use black U.L. tape to do all my transitions since there is no flap available but even the black tape is stapled, triple silvered, then pookied. This makes for a very solid, long lasting system.

Hope this helps.

Unless I'm mistaken, the "pookie" that fluffybunnysui refers to is mastic.

If your installer wants to use foil mastic tape, I'd go for it. The only caveat is that make sure it's one with the UL listing printed on it. These go on a lot cleaner than bucket mastic, but they're a good bit more expensive (~$30/roll for the Nashua or Polyken tapes).

I did a bunch of re-work after a leaky pooched install. The only thing that I found the plain foil tape was good for was sealing the longitudinal seams on sections of hard round duct. Conforming to any kind of irregular surface or the slightest bit of dust and it wouldn't stick.

The butyl backing on the foil tapes is a thinner version of the stuff that's in wide use for flashing tapes and roof membranes these days. It's good stuff and should stick tight.

foil tapes stick well to foil surfaces
mastic tapes seal most materials
wood to metal, metal to metal,
flex duct to metal, sheetrock to metal.

different tapes provide different sealing
on different surfaces.

I like hardcast brand mastic tape.
and use it to seal supply boxes to sheetrock
from interior of house. makes an excellent
long lasting seal.
surfaces must be clean and dry for tape
to adhere properly.
hardcast also makes paint on mastic.

why doesn't your contractor use mastic??

great pics fluffybunny..I've always used
the foil/paper tape with the nylon scrim
for ductboard and hard duct insulation.

best of luck.

My contrator wants to use UL181 foil tape with straps. I would perfer he use Mastic. He said it was complicated and messy. Messy yes. Complicated no. My guess is he does not want to use it because it is more time consuming than his method. Hence the old adage, "Time is money". It will be my sugestion that he use Mastic Tape. If that is a problem than that will be the deal breaker.

I think the plain foil tape needs near-perfect conditions to adhere well. Mastic would be a good backup like fluffybunnysui mentions. I'd bet the installer will balk at the cost of foil mastic tape.

energy_rater- is the Hardcast one a foil mastic tape? That was the brand I was remembering, but I looked a little and couldn't find it on their site. May have just been a poor structure to the site, but it had me wondering if maybe they didn't make it any more.

Thull...I agree...if areas are not clean and dry
the tape will not adhere.

it is worth the seal for the homeowner to buy the
mastic tape IMO.
I don't see what the problem with paint on mastic would
be..doesn't take a genius to work a paint brush.
to say that it is complicated...
messy..oh yeah! but complicated?? no way.

hardcast has a foil facing with red writing and a gray
mastic backing. also a white plastic strip that is a pita
to get off the mastic side of the tape, but it keeps
the mastic from sticking to the next layer of tape.
I buy it all the time at the hvac supply store locally
(coburns in La.)

also 3" straps with no more than a 1" sag in a 4'
section. ducts should not dip or have a lot of excess
duct..curves should be smooth and not restrictive.

guess you can tell I'm a ductwork kinda person.
too_often the ductwork kills the air flow.

best of luck

I tried the tape but it was not mastic tape. I purchased a roll of UL listed good foil tape and rather expensive also. I wiped down the ducts and installed. The tape worked great for a few months and it started to let go. I later after hanging out in here long enough purchased mastic and tried it, there is no comparison. I would take a chip brush and bucket of mastic any day over tape. I do not have experience with mastic tape... but I know the cheap chip brush and mastic is hard to beat.

Energy...that was my thought to buy the tape myself. How much tape would i need for a typical installation? Mastic tape is very expensive at $30+- a 100' roll.

two rolls.3"
one to be used at duct take offs on
the plenum, sealing the top of
the plenum.

takeoffs collars are round so tear the
tape into 4" pieces and use several pieces
to seal the take off. using one strip will
not seal. (been there done that..waste
of material) sometimes the plenum will have
a coating of oil, so make sure the surfaces
are clean and dry.

then once supply boxes are installed
before the grills are installed
seal the boxes to sheetrock ceiling
from inside the house.
cut the 3" wide tape in half into
1 1/2" strips, staying within the
area the grill will cover, put tape
on ceiling and fold into supply box.
there is a metal rim that the tape will
adhere to. press firmly to seal well
then install grills.

the take off collars, plenum and supply
boxes are the biggest source of leakage.

you don't say where your return air is located.
ceiling or r/a chase.
this is another leakage area.
if it is in the ceiling, from the attic
caulk all 2xs and then caulk 2x framing to
attic floor. from the inside caulk corners
and where 2x's meet.

when there is a rim of dust around the filter
grill where the filter is installed it is an indication
of r/a leakage. air bypasses the filter and collects
on coil.

if you have a return chase..we will have to
talk more about sealing that.

it is well worth your time to seal these areas.
if hvac company doesn't do it..take it upon yourself
to do so.

I think it is great that you are educating youself
as to what you want. Wish more folks would do the same.

best of luck