Distortions on Asphalt Shingles

Technical Bulletin #4

Current as of July 2021

Occasionally, asphalt shingles may distort slightly along their leading edge to create a small bump somewhere along the length of the shingle. Typically, the remainder of the shingle lays flat and looks fine in all other respects. These bumps may be more noticeable on certain roofs because of slope, sunlight, shingle colour, viewer angle, etc. These distortions do not diminish the life of the shingle. Often, the shingles' uneven appearance is caused by:

  • raised fasteners (nails or staples),
  • dirt, leaves, or other contaminant on the shingle sealant,
  • uneven deck, underlayment felt, or old shingle layers,
  • shingles damaged or bent prior to application.

These "fishmouths", as they are known in the industry, are merely aesthetic phenomena which can be easily repaired. The most common repair method used is a hot melt adhesive to glue the distortion down to the underlying shingle, thereby rendering the shingle flat. The sealant bond on the affected shingle should be broken first, and the repairs are most effective when done during mild (but not too hot) weather conditions.

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.