Blistering is common among membrane roofing systems. Blistering is when bubbles form underneath the roof’s membrane.
By learning what causes blistering, you’ll be better equipped to prevent it. And, if you’ve found blisters on your roof, we’ll show you some ways you can repair them!
What Causes Blistering Membrane
Blisters form when there are pockets of air or moisture trapped between layers of your roof’s membrane or between the membrane and the roof deck.
As the sun heats the roof, those pockets expand and stretch the membrane.
In severe cases, the membrane will actually crack when the pressure becomes too great.
Even if the roof membrane doesn’t crack, blisters are usually a cyclical problem.
That is, once they form, the membrane stretches permanently, which allows for even more air or moisture to infiltrate the membrane layers.
This causes even more expansion. Each time the sun heats your roof, there is the potential for the blisters to grow a little larger.
How To Fix Blistering Membrane
Many experts believe that unless blisters are showing signs of more serious damage, they’re best left alone.
However, there are certain circumstances in which you should repair the blister:
- The surfacing is coming off of the blistered area.
- The membrane itself has cracked.
- The blister is near enough to the seam that it may cause the seam to open up.
- The blister is in an area that receives foot traffic.
How To Repair Blistering Membrane
To repair a blister, cut away the membrane until you reach an area where the membrane still adheres to the roof tightly.
You’ll then need to reapply new membrane material – at least as many layers as you removed – over the blistered area.
Make sure that the new membrane extends at least six inches around the edges of the blister to ensure that your patch remains leak-proof despite the expansion and contraction caused by temperatures shifts.
How To Repair Blistering Membrane On A Bitumen Roof
Alternatively, on a bitumen roof, you may be able to cut an “X” into the blister and then peel back the loose membrane layers.
Fill the void underneath the membrane with bitumen and then press the membrane back into place.
Keep in mind that this particular repair method is only advisable if the membrane is otherwise undamaged.
Because blistering is common among some membrane roofing systems, you should make sure to inspect your roof at least twice per year.
Apply new coatings as needed, and make sure to repair any blisters that could cause a leak.
