Historic Non-Structural Detail: A Terrible Mistake

by Don Friedman on September 29, 2016

Kids, don’t try this at home:

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That’s a picture taken during brick replacement at a small 1870s building. As was common during the late 1800s and most of the 1900s, the roofing was flashed to the now-removed brick parapet with a heavy application of tar. In the picture above, you see the roof-joist ends at the bottom, the roofing tar-paper at the top, and the turned-up tar paper that was stuck to the parapet in the middle. Let’s look at a  close-up of the turned-up roofing:

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The tar ripped the faces off the brick of the parapet. Not only is this a problem for the brick, it cancels out any possibility that the flashing would do its job keeping water out. But really, the amazing thing here is that the adhesion of the tar to the brick is stronger than the bricks’ cohesion.

Putting tar on brick destroys it. It may waterproof it for a while, but it ultimately will destroy it.

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