In studying the causes of various types of blistering with a view to minimize the blister potential, much has been learned about the behaviour of blistering shingles. Typically organic asphalt shingles only blister where the exposure conditions on the roof include one or more of the following:
Regardless of cause, blistering can be of two basic types: small rash type blisters, ¼ inch (6 mm) or less in size, growing out of the coating layer, and the larger tent type in which the entire thickness of the coating layer is raised from the base reinforcement. Authorities agree that while these larger tent type blisters may cause premature failure of the material, the small rash type will rarely do.
Blistering would normally apply to organic felt asphalt shingles and is not considered an issue since the introduction of fibreglass asphalt shingles.
The information contained in this bulletin is for general education and is not intended to replace advice from a qualified contractor or direction on usage/installation from the manufacturer. Consumers should be aware of the safety hazards associated with work on roofs and, before doing so themselves, should consider following CASMA s advice of using qualified contractors. This bulletin may be reproduced with permission on condition that it be reproduced in whole, unedited, with attribution of copyright to CASMA.