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Blisters refer to raised surface areas over voids in a roof system which contains entrapped moisture. A common problem with asphalt shingles is blistering shingles. Asphalt shingles burn mainly because of either trapped moisture in the shingles or poorly ventilated roofs. During manufacture, moisture can be trapped within the shingle. When shingles on a roof have trapped moisture, they will tend to blister because when the heat from the sun heats the shingle, it heats up the moisture as well, resulting into blistering. Roofs, on the other hand, should have a sufficient ventilation system. Blistering can occur to roofs that are poorly aerated due to the intense heat. Blisters can be identified as they resemble little pimples in the roofing material and are often moisture associated.

Any  roofing company will tell you that even under perfect conditions, an ideal void-free roof cannot be laid. Voids come up due to uneven substrates, skips in bitumen skipping, curled felts, and entrapped debris. Blistering takes up two forms; blisters between the membrane plies, and blisters between the substrate and the roof membrane. Blisters between the substrate and the roof membrane occur when the pockets of moisture and air trapped between the substrate and the membrane inflate in the fast heat of the sun, displacing the membrane to form a blister. The blister is formed when the substrate material has little permeability. An increasing blistering between roof membranes and cellular foam insulations is because of the gasses being emitted from the cells of these laggings.

Blisters cannot develop without a topping up procedure that adds more moisture and air between the layers. As such, your roofing company will confirm that pressure levels calculated inside blisters are lower than those estimated from sealed systems. A vacuum within a roof will, therefore, grow due to the water vapor and air expansion. Built up roofing membranes are rigid and hence expand when heated. Any permanent deformation on the layer develops a space within the blister, causing air to enter into the enclosed vacuum through the tiny splinters in the bitumen mopping. Blisters grow when the increased pressure prevails over the tangential bond of the blister, or when the volume of the air sucked at night surpasses the volume of the air forced out during the day.

Blistering shingles are bad because they explode at the end. When blisters explode on shingle roofs, the granules become dislocated. Popping leaves the asphalt exposed to the ultraviolet rays of the sun. This exposure leaves that particular area of the ceiling at the danger of losing more and more granules. With natural weathering and time, the popped blisters area causes roof damage and leakage. When roof temperature increases, pressure inside the blister also increases. This intensification weakens the adhesion of the asphalt. When a blister stretches, it doesn’t shrink down to its initial size even when the temperature cools down. This results in water and air entering the blister causing growth, which will later lead to destruction.

There some measures that can be used to reduce blistering. Using dry materials in dry conditions is one measure. As such, when roofing, an local roofing company should close up concrete decks with high-quality air and vapor retarders, keep materials under tarps, and ensure that substrates are dry before using them. Another measure is ensuring contact between the materials. As such, one should use sturdy cover boards over cellular plastic padding to allow gas ventilation. Limiting foot traffic is also necessary for preventing blister breakage. Local roofing company contractors should also use specially designed vents which allow for fast repair.


Charlotte, NC

2015 Ayrsley Town Blvd Suite 202
Charlotte, NC 28273

Raleigh, NC

8805 Midway West Road
Raleigh, NC 27617

Louisville, KY

9850 Von Allmen Ct STE 201
Louisville, KY 40241

Nashville, TN

555 Marriott Drive, Suite 315, Nashville
Tennessee, 37214

Knoxville, TN

200 Prosperity Drive.
Knoxville, TN 37923

Columbus, OH

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