b'UPDATE IBLISTERREPAIRINBUILTUPMEMBRANE CArticle Courtesy of uruary1996.Contractors Guide, FebBlisters are spongy, raised portions of a builtzup roofing membrane. They result from the pressure buildup ofthe most common gases -being air and / or water vapor - trapped in the zmembrane systems. Blisters are usually caused by the delamination of the underlying membrane uplies of the built-up roof system. Thus, to permanently repair membrane blistering in a built-up roof system, a thorough un derstanding of the causes is necessary.orture has evaporated, hot bitumen is mopped Ill Encapsulated moisture or moisture vapor in the bitumen mappings can occur between the deck or roof insulation and the membranes, between the membrane plies. Several methodsinto the cavity and the membrane or memof repairing blisters have been attempted. Re branes that have been peeled back are pressed sults have ranged from complete success to al into the bitumen. Then, two or more additional most immediate recurrence ofreviewplies ofover blisters. Afelt are mopped into placethe cut of several methods can help determine whicharea. This method has possibilities in that whatwill most likely correct the problem.ever voids exist in the bitumen can be cor0The most economical orrected. However, success of this method deeasiest method used over the years has been to puncture thepends upon the complete evaporation of blister, inject either hot ormoisture and the expulsion of cold bituminous ma air. terial, and firmly press the blister down. It is0From experience in the field and laboratory BY BOB LACOSSE,CAEpossible this could eliminate the void left in thestudies, it has been determined that the most bitumen mopping or spreader and expel the air.effective method used to repair blisters is the However, it is questionable as to whether thecomplete removal of all the materials distorted existing moisture would be expelled. Jn thebyof the blister. All raised or septhe formation event moisture remains in the roof system, re arated membranes should be cut out with a currence of the blister is inevitable.sharp instrument. Care should then be taken @ Another easy and economical method in so no sharp edge remains where the material volves puncturing the blister and heating it withwas removed. In this area, the remaining mema moisture evaporator until the bitumen hasbranes should be tapered back from the cut reached a fluid state. The blister is then firmlyedge to reduce the unevenness ofsurface the pressed down, forcing out the entrapped airthat may be visible through the newly applied and moisture. This method has some possibili felts. Complete drying of the existing memties, but success is predicated on the elimina brane is important. Hot bitumen should then be tion of all air and moisture and the generation ofapplied in an amount equal to the number of ply sufficient heat to cause the bitumen to fill thefelts removed. The plies of new felt should existing voids. This method is questionable. Ifoverlap the cut area and be shingled away from sufficient heat is applied to cause resealing,the centerthe repair to achieve smoothness. of other materials within the system may be dam It should then be resurfaced or coated as the aged.final application. It is the consensus that this @}Probably the most widely used method,method of blister repair has greater chances of both currently and in the past, is to split thesuccess than those previously described beblister, peel back the raised membrane and ex cause all causes of the original blisters have pose the cavity of the blisterthe sun in an ef been eliminated. to fort to evaporate the moisture. When the mois-MRJune965'