We replaced our tar & gravel roof with torch-on roofing about 13 years ago. I went up on the roof last week after the snow cleared and I was alarmed to see lots of air pockets under the roofing. There are places on the roof where I didn’t want to walk because it was like walking on marshmallows. What is this all about? Is it a problem? If so, how can we fix it?

It is interesting to note that this “blistering” was a common problem with tar and gravel roofing back in the day when it was the king of flat roofing products. But this problem is not nearly so common with the new torch-on roofing. However, it does happen occasionally and here are a few possible explanations with a note of appreciation to the experts Ross and Ray at Heritage Roofing for their input.

In both tar and gravel and torch-on roofing, the blistering is caused by delaminating between the plies or layers of roofing felts or sheets.  In tar and gravel applications this can happen because the “mopped on” tar layer between the felts was too cold or poorly applied. With torch-on roofing the reasons for blistering are different, but the end problems similar.

When torch-on roofing was becoming popular as an alternative to tar and gravel roofing some 15 years ago, the manufacturers hadn’t perfected the way the removable plastic backing sheet released from the underside of the “top sheet” as it was rolled out and torched to the “base sheet”. Occasionally pieces of this plastic backing sheet would remain on the underside of the base top sheet affecting the quality of the weld between the base and top sheets. Water vapour often had the opportunity to build up between the two plies, swelling, blistering and eventually delaminating the sheets.

Can these blisters be repaired? The good news is yes. And it is not as difficult and, therefore, not as costly as repair of blisters on the old tar and gravel roofing. However, to avoid a costly roof replacement don’t let these blisters go unrepaired.  I recommend that you contact a reputable roofing company that specializes in “flat roofing” for an estimate and a time frame to conduct the repairs.