I remember reading a thread in here about roof shingle manufacturers stating that any pressure greater than 300 psi would void their warranties and that when a sample shingle is sent back to their lab for testing (in a warranty claim) they have a specific test to determine if it was subject to greater than 300 psi.

I have been searching through here, but alas, I can not locate the thread.  Anyone have any idea where that can be found????

Thanks.

They really don't put antyhtthing in writing. they will just tell you not to use high pressure. All manufactures have in house and third party testing labs, accelerometers that can tell if the shingle has undergone mothat ham natural pressure and exposure. In tat case most will walk from the warranty.