Triple Crown - Blisters

Commercial Roofs | Metal Roofs | Blisters | Brochure | Details | Flashing
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How They Occur and How To Prevent Them

In the belief you, our customer, will better understand the soundness of our methods of roof repair and installation, we feel it is to your interest to better understand the nature of some of the problems we identified on your roof.   With this in mind, let us explore one of the more common roof problems – blisters…

Ninety-five percent of all inter-ply blisters are the result of excess moisture being trapped in the roof system at the time of original installation.   We say excess because all roofing membranes contain moisture.   As a matter of fact, the moisture is introduced into the membrane (felt) intentionally at the time of manufacturing.Excess moisture is the cause of blisters.   The excess moisture may have been introduced into the system in several ways:

• Lack of quality control at the time of manufacturing.
• Membrane, while stored were exposed to moisture or high humidity prior to installation, either before delivery to the jobsite or at the jobsite.
• The roofing system left open during rain or snow.   Ply felts, such as 15 or 30 pound felts are not coated in manufacturing.   If a sealing coat is not applied to the top surface of the installed felts, moisture can be taken into the system.    A common occurrence is is a rain after the felts are installed, but before the top coat of asphalt is applied.

Regardless of the cause, once the excess moisture is in the system, and the top sealing coat if asphalt is applied, the moisture is trapped and the ingredients for premature roof failure are in place.   The remaining element necessary is time.

When the roof system is cool, the trapped moisture is solid – water.   But, when the sun heats the roof system, the moisture turns to vapor; and, in doing so, expands, creating the blister.

Two misconceptions need to be dispelled here.   (1) Blistered areas are not leak areas, originally.   The fact that the vapor cannot get out is proof the roof-top moisture cannot get in, originally.   (2) Blisters do not remain constant, but come and go.   This is why, if not corrected, they are ultimately destructive of the roof system.   On a cool morning, a roof surface may appear smooth, but that hot afternoon, the same area may show signs of considerable blistering.   It is the raising and lowering from the hot/cold cycles that cause the destruction.

When a roof is new, the flexing in the blistered area does not appear to have a detrimental effect.   However, as the roof becomes older and the membranes become more brittle, cracks begin to occur at the edges of each blister.  

An Ounce Of Prevention Is Worth A Pound Of Cure!