The photograph below shows a field of blisters that have formed on a flat roof of a house in central London. Just as for the case of the pavement asphalt blisters conventional wisdom has it that these blisters are the result of the build-up of gas pressure beneath the asphalt sheet. Problems with such an expalnation follow those outlined in the previous blog for pavement asphalt. In contrast, a thermal upheaval buckle explanation is entirely consistent with the geometry of the blisters, again dominated by almost pure circular planforms
The flexural cracks over the upper regions of the blisters at times penetrated through the thickness of the asphalt, again undermining the gas pressure hypothesis for the formation of the blisters.
Scale of the blisters can be measured by the 20p coin having a diameter of 25mm.
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