There are several causes as to why one might have to deal with blisters on a flat roof with heat and the sun being the main causes but it also points to the presence of moisture.
If there are too many blisters on your roof, then it’s probably time to call for the help of a professional but if it’s one or two, here is a list of steps that you can follow to fix it yourself:
Step #1: If you find any dirt or gravel located in and around the blister, make sure you clean it first.
Step #2: Using a knife, ensure you release the pressure from the blister by slicing through the top layer.
Step #3: When you’ve made that hole, now feel for moisture in the hole you’ve made in step 2. The reason why you do is you have to look for leaks in the flashing or which are located in the general area of the blister and get them fixed immediately.
Step #4: Now, using a putty knife, apply plastic roofing cement in the cut and around it as well for by at least 2 inches in all directions.
Step #5: Now you have to cut a patch of asphalt shingle or roll roofing that is about 2 inches larger, and slide it into the cut. Once this is done, press it towards the roofing cement that you added in the previous step so as to cover as much area as possible inside the cut. Now, add roofing cement over the blister so as to seal it, and make sure to apply more cement (at least 2 inches) beyond the edges.
Step #6: Now, you can sweep the gravel back over the patch.