# which type of sealant is a better choice silcone or roofing cement?



## RIDGERUNNER30 (Oct 26, 2010)

soon as this weather breaks , I will be ready to cut out the roof and install the chimmey, I have a metal roof and had to order a rubber boot kit to install this chimmey system the instructions state to use a silcone sealant under the edges of the boot to give it a waterproof seal. my question is would roofing cement or (aka) black jack be better to seal the boot with or silcone? which one would last the longest  they sell black jack in tube form to be use in  clauking gun.


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## Retreadsme (Oct 26, 2010)

I personally have had very limited satisfaction from using roofing cement when attempting to bond rubber to anything.  My recommendation would be to use a high quality silicone for the application you are describing.  Others may get better mileage.


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## Bubbavh (Oct 26, 2010)

I would use high temp. rtv over black jack on a metal roof. The only time I ever use black jack is to reseal shingles after a repair!


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## btuser (Oct 27, 2010)

Roofing cement is going to dry out.  Silicone will remain flexible  Metal moves around a lot.


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## Smokey Bear (Oct 27, 2010)

Definitely use the silicone or a urethane in that application. The blackjack could deteriorate the rubber gasket. Make sure the silicone is an exterior grade product there are a lot of different ones now.


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## Nic36 (Oct 27, 2010)

Like Smoky said, I think stuff like Blackjack is not recommended on rubber, as it dissolves it. I have had good luck with the GE 100% silicone for sealing the seams and pipe joints of my metal chimney.


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## precaud (Oct 27, 2010)

Agree with Smokey, silicone or PU. One downside to silicone is nothing sticks to it if it ever needs repairing. I tend to favor PU caulks for that reason. The PL brand at home depot is excellent stuff.


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## Ronmbucket (Oct 27, 2010)

On A rubber boot to a metal roof,I would use polyurathane caulk. Sika-Flex works best and is availible at masonary supply houses. Quad Caulk is good too,availible at roofing supply houses. Avoid Lowes and Depot.


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## semipro (Oct 27, 2010)

I'd consider urethane as I think it has advantages over silicone.  I wouldn't even consider using the tar-based stuff.


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