What Can We Tell from This Photo? (Case Study 5)
This is an exercise to develop the abilities of observation.
What can one know from examining this photograph?
- The cohesive failure of the asphalt in the mat, especially at the right end, indicates that the force required to lift the tab was substantial. A cohesive failure is where the fracture occurs within the asphalt material of the shingle mat rather than between the sealant and the mat.
- The large amount of undisturbed debris along the right edge of the tab indicates that the tab was lifted and set down relatively quickly and that the debris was not exposed to high winds that would have disturbed the particles of debris.
- The debris adhered to the sealant indicates that the sealant remained tacky for some time after the failure allowing particles of debris to adhere to it. This shingle tab was not unsealed for an extended period of time, but if it had unsealed, it was prone to re-sealing.
- The crack on the underside of the tab is indicative of a fracture from hand (or finger) lifting. Wind is not capable of lifting such a short width of the tab and fracturing the mat without causing much collateral damage.
- Where an cohesive sealant failure occurred (fracture within the sealant) the exposed sealant is a dark black color indicating that it occurred relatively recently and that the tab was very well sealed prior to its failure.