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The Inspector's Journal

Darkness at Modified Bitumen Seams


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I was unable to reach the top of this roof with my ladder so I took a blind video over the edge with my camera on a tripod extension. I'm a little confused at all the darkness at the modified bitumen seams. I think it had rained a little bit the previous evening.

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It's not bleed. Agreement all around on that one. It's not heat from the torch either. It's the tar from the hot mop.

It's not a cold applied application. It's SBS; it can go down cold with adhesive or laid into hot mopped asphalt.

SBS mod bit, when laid into a hot asphalt and a base sheet, has seams looking like this. Google "SBS modified bitumen images". You'll get a few looking just like this.

Also, the powdery white stuff doesn't wash off. It's SBS. It will subside slightly, but it doesn't go away. At least, it doesn't go away for a very long time.

Following image screen grabbed from googling SBS images.....

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  • 2 months later...

It's heat from the torch. Here's one that I saw yesterday. It was just torched down the day before and, despite the rain at the time of the inspection, the white powdery stuff had not yet worn off - but it will very soon. I could rub it off with a single swipe of my finger.

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Can't you see the difference between your pic and the OP? OP field looks like SBS in tar and the walls (which no one mops cuz you can't) is over torched. Yours looks like over torched.

I can't believe that we're both talking about the same OP picture. The whole thing is torched, not just the parapets.

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Maybe. If it is, someone was surprisingly consistent in their overtorching ****up.

Look at the difference between the overtorch on the parapets and what you're alleging is the overtorch on the field. Two entirely different patterns. The OP has nice relatively even lines of darkness, exactly like a mop job. The parapets have that blasted look, especially a the kant where it turns up the wall. I'd have to touch it and see it to know for sure, and until someone does, this is all conjecture.

We've got thousands of these, maybe tens of thousands, all over Chicago. They don't do it anymore, but it was standard practice for years. Mopped SBS, white powdery stuff that stays powdery for a long time, etc. exposed tar turns a different color.....they're everywhere. They look like the OP. Nice even lines of overmop.

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