i just did one back in sept. or oct. 2008 that was the balls.its called dekathane from liquid plastics out of conn.,i used it right one the helicopter landing pad @ southern nh medical center,the pad is actually a concrete roof deck over the radiology dept.this stuff was exp.,$7.00 per sq. ft./thats $700 per roofing sq.just for the materials.it comes in all different colors & liquid plastics gives a 50 yr. warranty.im 40 now so i dont have to worry 50 yrs. down the road.
cut out the blisters & patch,scratchbar were its alligatoring,dump a tremco resatch on it, & alumicoat that.you definently dont want a go over w/ tekdum, it cant hold the weight & you definently dont want to rip it.because then youll have to auger your insul back down & that sucks.never mind trying to find tekdum if you have to replace some.
The blisters are caused by moisture trapped between the layers of membrane. As corry stated, you need to cut out and patch the blisters (do this on a hot sunny day, so you are likely to get them all). If the existing membrane is acceptable as a substrate, you may be able to install another mod. bit. over the existing. If not, then you may either want to look at coatings (elastomerics, like urethane or acrylic if you have adequate slope) or spray polyurethane foam (though I am not the one to talk with about SPF).