# How long to let mastic on collar dry



## ben's plumbing (Oct 6, 2011)

i believe water based mastic ..2-4 hrs dry time ... what type do you have?


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## tearitup (Jan 4, 2015)

It's Design Polymerics (DP 1030) - water based, fiber reinforced.
http://www.designpoly.com/sealants.htm

Looked at spec sheets for the 1030 mastic & others they list.
All their duct sealants said, "24-72 hrs cure, depending on temp / humidity." "_Allow at least 48 hours before pressure testing."
_Not sure what type pressure tests (commercial systems?) - doubt it applies to typical residential.

This DP 1030 skinned over fairly fast & in a hot attic dried to touch in maybe < 1 hr (didn't check till later). "Dry to the touch" and dry / strong enough to pull on the joint - while connecting duct, could be different things.

Not being sure, I decided not to chance connecting the flex today.
But, my free help & muscle (son) went home. "Capped off" the new collar & southern engineered connecting the old duct (different collar) to the replacement wall boot, to get AC back. Today's high - 95.

Found this "RCD Corp #8 water based mastic" - says,
"cure to 4lbs./in. tensile joint strength at 50% RH and 70˚F - 5 hours."
That's faster, but not fast enough for some pro repair jobs.
 
Pros must use faster drying stuff. Or Design Polymerics' instructions are way off.


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## Dak Man (Jul 4, 2015)

what does it matter? It'll dry in a few days and until it does it'll do it's job wet. . I just had to redo a transition form furnace to coil after three days of original install. Mastik was still wet, but didn't leak air. 

Mastik does not know it's mastic.


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## nap (Dec 4, 2007)

if you do not have massive air leaks under it, once it sets to a non-tack state it should be able to handle what it is expected to do. If you have a big air leak expect to find a balloon on the side of your duct. 



I would tell you how long the pro's on my job typically wait but they wait simply because it takes months and months to get from starting to pressurizing the ducts so it is not indicative of how long you need to wait.

take a bit and spread it onto something smooth and flat and let it set. Check it after a few hours to see what it is doing. You can usually find a point where it is solid enough to be functional well before it is completely set. 


but are you actually pressure testing though? Running a system is very different than actually pressure testing a system. When testing you actually and intentionally close down the outlets to test for leaks. If you are simply operating the system with the outlets all open such as they will be when it is running, the mastic generally is not exposed to much pressure.


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## tearitup (Jan 4, 2015)

Dak Man said:


> what does it matter?


Depends. So once Dak installs a collar w/ flange into rigid duct board, smears mastic over the flange & duct board (? using mesh tape), then he starts connecting flex or metal ducts right away?

Until most adhesives are cured, it's easier for any movement to weaken the bond to the substrate.
My duct board flexes easily. May depend on the amount of movement at a joint by stretching duct, tightening zip ties, etc.

Maybe in practice, doing this with uncured mastic never weakens its adhesion?



nap said:


> take a bit and spread it onto something smooth and flat and let it set. Check it after a few hours to see what it is doing. You can usually find a point where it is solid enough to be functional well before it is completely set.


Thanks. I've done that (unintentionally) in the past. Gotten excess mastic where didn't belong. Even after dry to the touch - but not fully cured, it's often easy to pull it off. After curing, very difficult to remove.
That was my concern - since uncured mastic is easier to remove, whether flexing a seal / patch might weaken the bond.


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## ben's plumbing (Oct 6, 2011)

2-4 hrs is dry time to touch ..24 hrs before running furnace..full cure 36-48 hours...its worked for us..


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## tearitup (Jan 4, 2015)

ben's plumbing said:


> 2-4 hrs is dry time to touch ..24 hrs before running furnace


OK, thanks. 
Do you start connecting flex or pipe to masticed collars (on duct board), as soon as "dry to the touch" (2-4 hrs) & no problems messing up the mastic?

On waiting 24 hrs before running furnace, if you mean heat (not AC) - I can see not wanting to get uncured mastic too hot.


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## beenthere (Oct 11, 2008)

Usually easier to attach the flex, and then mastic the collar.


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## ben's plumbing (Oct 6, 2011)

yep we attach the flex 1 st ...:thumbsup: but if your careful i would guess you could do it after a few hours....however you do run the risk of breaking the seal:yes:


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