b'hesive cures (dries) over the top of a gypsum cover board. But in other roof system types, a void could be present as a result of various issues, including a wet substrate, and mois- When in doubt, ask the manufacturer what turewillmigrateinastheblister grows to equilibrium.Another major point to consider inblisterformationandgrowthis temperature.Numerousvoidsarethe materials moisture content should created when a sheet, such as a self-adhering vapor retarder, is applied to a concrete roof deck. It doesnt help that many vapor retarders have poorbe and how to test it; preferably, get this solar reflectivity and when exposed to sun they dramatically rise in tem-perature.Asdiscussed,iftempera-ture increases, pressure and volume need to rise to balance the equation. information in writing.The solution for a blistered vapor retarder is to place insulation over it. The insulation will regulate the tem-perature of the vapor retarder; the blisters should collapse as the tem-perature component is removed and the vapor flow can return to the in-terior of the building to be handledcause some cover board and insula- and application techniques to avoidWatervapormakespressureIhaveforensicallysampled by the HVAC system. This phenom- tion materials can arrive at job sitesthis altogether or lower the chance ofchanges higher in a blister. blister gases in the field as to find enon has been observed in the field. withelevatedmoisturecontents.it occurring.If the blister is closed, considercausation and to see whether cold Avoiding Blisters This means a field crew needs to beleaving it alone. adhesivesweretheculprit.But vigilant and inspect products as theyMain PointsIf a blister is in a high-traffic Earlyresearchfocusedonuni- when blister gas was subjected to formhotbitumenapplicationtoarrive for excess moisture and protectBlisters on roofs can appear forarea, it may be prudent to re- Fourier Transform Infrared Spec-avoid creating voids. This still is thestored materials. When in doubt, askany number of reasons, but it willpair it even if still closed. troscopy, it consistently returned case. Mopping asphalts are not whatthe manufacturer what the materi- help to remember these tips:Ifablisterhasrupturedresultsofnitrogen,oxygenand they used to be, so this now may beals moisture content should be and A blister needs a void to begin(opened),hasexposedthewatervapor.Therefore,research more difficult. But the point is stillhow to test it; preferably, get this in- or, at a minimum, a disbond- membranereinforcementand field experience have routine-valid. Applying bitumen safely at orformation in writing. edarea. orhasfatiguecracksform- ly shown blisters only contain at-preferably above its equiviscous tem- Asdiscussed,someblistersare Substratemoisturecancreateing around it, cut it out and mospheric gas and water. Stay safe perature with uniform coverage willrelatively temporary in nature. Re- voids or the disbondment nec- repairthemembraneper lessen the chances of a void. movetemperaturechanges,andessary for blister formation. manufacturers guidance and/ out on theroof.blistersshouldcollapseandelimi-Blistersneedatemperatureor NRCAsRepairManualMattDupuis,Ph.D.,P.E., You also can avoid blisters by not installing roofing materials over wetnate themselves. Additionally, somechange to create the pressuresfor Low-slope Membrane RoofispresidentofSRIConsultants, substrates. This can be difficult be- manufacturers can suggest productsneeded to grow. Systems, 2nd Edition. Waunakee, Wis. 87 Bakersfield St., Toronto, Ontario, M3J 1Z4 Tel: 416-787-0649Fax: 416-787-0640 Email: service@crawfordroofing.ca www.crawfordroofing.caIndustrial Commercial Institutional Roofing Solutions - PMI Programs- Modified Bitumen- Built Up Systems - Metal Roof Systems- Waterproofing- Restoration- Emergency Services- Roof Anchors- Single Ply - Roof Top Decks- Sheet Metal- Inverted Committed to Safety, Quality & Service for 40 years Services Fully Bonded & Insured ORN THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ONTARIO ROOFING NEWSISSUE 3 202417'