I got a ten yr old GAF Rubber Roid granulated cap sheet over my shop. Took some hail damage. Roofers are going to torch a new granulated cap sheet to the old. I wanted the old surface blown clean then primered. They don't think they need to primer. Should they are not ??
Yes at the very least you need primer.Degranulating is always better,but more time consuming.Before priming it should be thoroughly cleaned.If they are not priming the membrane will only be stuck on the laps.Phone the manufacturer or a qualified roofer and get there opinion as well.