There are several reasons, but the most common reason is that the coating/paint cannot stretch with the movement of the metal panels.  Metal panels expand and contract with changes in outside temperature.  

Want to know if your roof coater is using a formula designed for roofing?

Simple–test is take a chip of the roof coating:  

If the chip snaps when you bend it, then the coating is a stiff paint and the material will flake.

 Roof Menders, Inc, of Conshohocken, PA
610-941-1051
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