You may be asking yourself, “What can I expect a roof to look like as this aging process takes place?” One or more of the following conditions may occur over time:
As the asphalt hardens over time, the granules which were once securely embedded begin to break away. Occasionally you may have seen the coloured granules in gutters. Also, as this hardening advances, the asphalt layers begin to shrink. Of course, all of this is occurring at a microscopic level and is not something which will be noticeable on a daily basis. As the asphalt layer shrinks, it is being countered by the shingle reinforcement, which resists shrinking.
We now have a situation in which the top and bottom coatings are shrinking and the reinforcement is remaining stable. As a result, the edges of the shingle may begin to curl over time.
Another manifestation of the normal aging process may be the development of surface cracks. For example, as the flexibilizing oils of the asphalt are depleted due to heat, the shingle becomes more brittle, to the point where surface cracking may appear. The stresses created by thermal shock and the movement of the roof deck also increase the likelihood of surface cracking.
During the course of natural weathering, small bubble-like raised areas known as blisters may appear on the surface of the shingles. The blisters may be small and pea-sized or as large as a quarter. The blister may be open, exposing the asphalt, or closed. Blisters frequently result when minimum ventilation requirements are not met.
Finally, over a period of time, shingles may develop dark brown or black streaks that are sometimes mistaken for soot, dirt, moss or tree droppings. In actuality, this discolouration may be caused by algae growth. Although most roofing systems are susceptible to algae discolouration, it is most readily visible on white or light-coloured shingles.