I've got blisters on my shingles

[CheckItOut]

I see this every now and then. On one new construction house some time ago, the shingle mfg gave the buyer a letter stating that this was a manufacturing defect and it would not affect the life of the shingles. Confident, they doubled the warranty.

These blisters never appear on the entire roof - maybe just one side (maybe sun exposure plays a roll).

Just curious if anyone has a definitive cause and knowledge of how, if at all, this might affect shingle life.

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[Jim Katen]

I see this every now and then. On one new construction house some time ago, the shingle mfg gave the buyer a letter stating that this was a manufacturing defect and it would not affect the life of the shingles. Confident, they doubled the warranty.

These blisters never appear on the entire roof - maybe just one side (maybe sun exposure plays a roll).

Just curious if anyone has a definitive cause and knowledge of how, if at all, this might affect shingle life.

I call them rash blisters. As far as I can tell, they look ugly but they don't affect the life of the shingles. I see them fairly often in all stages from the early stage in your picture to the stage where they're completely sheared off and have left little pocks all over the shingle surface. I've never seen a roof leak because of them. My own roof developed these blisters one year after I installed it. It's now 17 years old and doing fine. The blisters have actually settled down and are barely noticable anymore. It's a curious phenomenon.

One manufacturer's rep told me that they were caused by the presence of moisture in the fiberglass matt before the asphalt was applied. This might be true. But I've also seen roofs were rash blisters were present only in locations where lots of water washed over the shingles.

Here's a tech bulletin on the subject from CASMA:

Download Attachment: RashBlisters.doc

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[asihi]

Most shingle manufacturers will call blistering normal and cosmetic. The problem comes in when they open, exposing the matting. Here's what Tamco has to say http://www.tamko.com/Portals/0/document ... -29-09.pdf