I’m pretty sure that I’ve read instructions on how to do a seam from two different companies.
1) Prime the overlapping surfaces
2) Apply the cement, let dry
3) Apply a bead of in-seam sealant a couple of inches off the inside edge
4) Press it down carefully, no bubbles
5) Apply a bead of lap sealant
Now, while I’m on the subject, my memory is that one set of instructions left out the in-seam sealant. Could that be right?
But more importantly, are there any systems that dispense with the final step of the lap sealant? I ask because one of the local roofers that does a lot of commercial rubber roofs apparently only uses the lap sealant in particular cases. I’ve been on a couple of his roofs and he isn’t using five percent of the lap sealant that I would’ve guessed. I haven’t figured out what determines why a particular two inches gets sealent and the seam to either side doesn’t.
I’ve been asked to fix a leak and my best guess is the seam has no lap sealant.
Rich Beckman
Replies
Rich, the instructions on my can of lap cement say to clean, glue, and press well, but nothing about a bead of adhesive in the lap, only at the raw edge.
It's warm enough there to do that ??? I'm jealous...
No, Splinter, it's not warm enough today (lots of snow today!), but it was warm enough a couple of weeks ago and will be again by the end of the week.
Rich Beckman
Dear Rich,
I agree with SG about the inside bead of caulk. Have never seen that and wonder if the caulk would cure. But no other trade is more susceptible to "local custom" than roofing.
The rubber tech reps want an untooled bead of caulk to straddle the seam joint. They say it prevents UV degradation of the seam glue, ties down the lap against wind, and provides one more water barrier in the joint. They want a bead on ever inch of every joint including boots and patches. I think they want to sell more product. Lots of commercial roofers will skip it.
Not one of my joints ever depends on the caulk to be watertight, but I do caulk them all. To keep my license, the reps reserve the right to inspect any roof I install. So I fuss. We do rubber all winter, sub-zero won't stop us. It does help to have blow drier. A few snow flakes will kill the glue though.
I don't think you'll have much luck depending on caulk to fix a leak. If you see a bad length of joint, you can pull it open, clean up, and reglue. If there's an isolated spot in a joint, it's best to patch the joint with uncured flexible membrane. Other patches can be regular EPDM sheet.
With lots of goopy work pants, Fred
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3) Apply a bead of in-seam sealant a couple of inches off the inside edge.
I never heard of this one.
These days, the main reason why you don't see lap sealant is that it is not required with the adhesive tape which has replaced the rubber to rubber sealant. Around here, (PA) nobody uses rubber to rubber sealant anymore except in special situations. The tape saves lots of time. (and lap sealant) This is for a Carlisle system, but it is my understanding that they are all the same.
Carlisle requires the inseam sealant or it voids the warranty. But I haven't heard of it from other manufaturers. So I think your memory is intact, Rich.
Good luck finding that leak.
Tom