b'Roof Blisters Photo 1: Plate, or pancake, blisters are the size of a dinner plate and one continuous air space. They can grow to be large in size.Back to the Start By Matt Dupuis,Photo 2: Linear blisters can range from several feet in length to 20 or 30 feet long. They are commonly found at the side laps of sheet membranes.Ph.D., P.E. Roof blisters have aThefollowingarticleoriginallybeingmoppedonasubstratedur- addressed blisters was published just appeared in the September 2024 is- ing a cool morning. This is a result,after World War II. Professor Clar-sue of Professional Roofing maga- in no small part, of the shift at theenceLund(thesameC.E.Lund long history in thezine. It is reprinted with permissionturn of the century from asphalt towhose research helped establish the from the National Roofing Contrac- single-plymembranesandlow-rise1:300ventilationratioforsteep-tors Association. foamadhesives. sloperoofing)attheUniversity roofing industry T here are new people enteringtoBut for those who still work withofMinnesota,Minneapolis,pub-the roofing industry, whichhot asphalt, one risk is always pres- lishedPrinciples Affecting Insulated isgoodandnecessaryasent: blisters. Roofing workers usedBuilt-UpRoofs in1952.In1959, ourindustrycontinuestoknow how to spot a blister, re- JamesMcCawleysbookRoofing growandreplenishthoseretiringpair a blister and how to avoid mak- discussed blisters in more common fromtheranksoftheoldguard.ing them. But even that knowledgetermsandexpandedonthetopic. Butthereseemstobeaproblemisfading.AndbecauseblistersareHowever,McCawleyheavilyrefer-conveyingsomelessonslearnednotuniquetoasphalt-basedroofencedLundswork.Interestingly, andinformationgatheredamongsystems, I would like to review blis- theybothidentifiedhowwater roofing contractors, consultants andter research, types of blisters, whatvaporexacerbatesblistergrowth manufacturers alike. causes them and how to avoid them. andformation.Many new to the industry mayIn 1960, the National Research not have wielded a mop loaded withResearch Council publishedA Study to Im-hotbitumen,knowtheunmistak- Blisters have been a topic in roof- proveBuilt-UpRoofs inwhichthe able smell of a hot kettle, or heardingresearchforalmost100years.paper A Theory of the Mechanism the snap and crackle of hot asphaltThe first publication I know of thatof Blistering by Warren Warden was 12ONTARIO ROOFING NEWSISSUE 3 2024 THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ORN'