Comments on: How to Repair a Leaky Roof Vent Pipe Flashing – Part 2

By: Bob Jackson

Bob Jackson — Wed, 21 Dec 2011 19:05:33 +0000

> I also have the roofer apply the Sonalastic sealant between the area where the plastic part
> of the boot made contact with the vent PVC pipe as extra precaution. Will that be a problem?
It wasn’t necessary to apply sealant there. The boot is designed to hug tightly around the vent pipe to make a watertight seal. The sealant won’t prevent the boot from cracking over time due to UV light damage from the sun. The rain collar is your best protection *in addition* to the boot. The rain collar “floats” freely as it’s only attached to the vent pipe, experiences no stress due to heat contraction/expansion of the roof and shields the vent boot from UV damage.

> Does the chemical in the sealant cause any damage to the PVC pipe?
The sealant won’t bother the PVC vent pipe. PVC is very resistant to most chemicals.

By: Q.L

Q.L — Wed, 21 Dec 2011 18:49:31 +0000

Finally got roofer back to redo the job. Beside having him sealing around the edges of the boot, I also have the roofer apply the Sonalastic sealant between the area where the plastic part of the boot made contact with the vent PVC pipe as extra precaution. Will that be a problem? Does the chemical in the sealant cause any damage to the PVC pipe? Thanks!

By: Bob Jackson

Bob Jackson — Sun, 04 Dec 2011 13:30:09 +0000

The DAP 3.0 Roof Sealant will be fine for sealing the nail heads.

> For the DAP sealant, that can be scraped off even after more than a week after it was applied
> since the roofer prob can’t make it back till the coming weekend?
A property of silicone & latex caulks is they are easy to scrape or rub off even when cured. Scrape off what you can with a small putty knife, the rest will rub off with your thumb. You need a clean surface for the roof sealant to adhere directly to the flashing.

By: Q.L.

Q.L. — Sun, 04 Dec 2011 04:39:04 +0000

I couldn’t find the Sonalastic sealant at the local store. I might order it online but that will take time. Can I substitute it with DAP® 3.0™ Advanced Blacktop & Roof Sealant with Kwik Dry® Technology (http://www.dap.com/docs/tech/00010054001.pdf) being sold at Home Depot?

For the DAP sealant, that can be scraped off even after more than a week after it was applied since the roofer prob can’t make it back till the coming weekend?

By: Bob Jackson

Bob Jackson — Fri, 02 Dec 2011 15:54:59 +0000

I'd have the roofer come back out, scrape off the DAP ALEX PLUS and reseal the nail heads. A dab of the TAM-PRO PREMIUM SBS Q-20 asphalt flashing cement on the nail heads would've been OK, so I wonder why he used DAP instead? The risk with the DAP caulk is it may peel or crack after a couple of seasons, but it's not like it's an emergency. It's more about a doing a quality job and using materials that have comparable service lives. If rain water worked it's way around the nail head, what'd you see is a water stained area under the roof deck from inside the attic, which could over time deteriorate as the glue in the OSB or plywood deck failed. If you had your roof reshingled down the road, the next roofer would say that section of roof deck needs to be replaced for an extra charge.

By: Q.L.

Q.L. — Fri, 02 Dec 2011 00:47:13 +0000

Thanks Bob! Do you have any suggestion? Should I have him come back to take out the DAP Sealant and reapply the Sonoplastic NP1 to the nail heads?

He did apply the TAM-PRO PREMIUM SBS (http://www.tamko.com/Cements-Coatings/TAM-PRO/ProfessionalMastics-Cements-SBSAdhesives/Q-20PremiumSBSFlashingCementTube) under the bottom tab of those shingles that were raised to install the flashing.

I did ask him to apply the TAM-PRO Premium SBS to the nail head as well but he said the DAP sealant is good enough.

By: Bob Jackson

Bob Jackson — Fri, 02 Dec 2011 00:07:57 +0000

Roofing applications are not listed in the "Suggested Uses" section of the DAP® ALEX PLUS® Acrylic Latex Caulk Plus Silicone technical bulletin. Whereas the SONOLASTIC® NP 1™ data sheet states under the "Where to Use" section (partial list follows): * Roofing * Wastewater treatment plants * Dams * Spillways and storm drains * Wetwells and manholes * Interior and exterior * Above and below grade * Immersed in water * Clay & concrete roof tiles A key product spec. in my opinion is the "Joint Movement Capability": * +/- 35% for the BASF NP1 * +/- 12% for the DAP ALEX PLUS because roofs expand and contract a lot between the cold nights and roasting hot sunny days. Given that the DAP ALEX PLUS product is not specifically rated for roofing applications and the wide variety of high performance roof-rated caulks available at roofing supply stores, I'd be disappointed with your roofer.

By: Q.L.

Q.L. — Thu, 01 Dec 2011 22:55:00 +0000

Your post is very useful. The roofer that I hired used DAP® ALEX PLUS® Acrylic Latex Caulk Plus Silicone to seal the nail and gap between new vent boot and the pipe since he had to tear off the inner ring to fit in the pipe. Is this type of sealant sufficient enough?

By: Dave

Dave — Tue, 29 Nov 2011 21:06:38 +0000

Thanks Bob,

Certainly will do as you advise.

By: Bob Jackson

Bob Jackson — Mon, 28 Nov 2011 22:34:34 +0000

I’ve seen roofers do exactly what you describe – it’s quick, inexpensive and avoids disturbing the shingles when a proper rain collar isn’t available or the weather is cold and the shingles may crack.

The petroleum-based sealant can attack the vent boot rubber. Check it in a week and again in a few months. I doubt it will crack immediately but will probably shorten the lifespan of the boot. Pick a warm day next Spring to replace the entire boot and add a rain collar.