Roofer torched out wrinkles in a flat roof and left bare bitumen. Is that a proper repair?

The owner described the job in a post on Reddit's r/Roofing: the roof covers an extension, it does not leak, and the warranty still runs. The question is whether the smoothed, bare patches can stay as they are. On a granulated cap sheet the granules are the weathering surface. GAF, which makes torch-applied membranes, says on its blog that a granule cap sheet gives the roof more resistance to UV.

Reheating wrinkles is a normal step. The same GAF article tells installers to check new membrane for wrinkles or lifting and reheat it where needed. The risk is heat beyond that point. The Canadian Roofing Contractors Association's reference manual lists the signs of an overheated sheet: granules sinking into the membrane, bitumen melting away until the reinforcement shows, and waves in the laid sheet. Where bitumen bleeds out at laps, the manual says to hide it under matching granules bedded in reheated bitumen.

Ridges and buckles that are not cracking and sit outside walkways are best left alone and watched, the CRCA manual says. When a repair is needed, the roofer cuts the ridge, re-bonds the loose material and puts on a patch of like material at least 6 inches (150 mm) larger on every side, then embeds granules at the edges. Karl Schaack, writing in IIBEC's journal Interface, said granules pressed into bitumen bleed-out at laps delay cracking there, and cracks that start in bleed-out can spread under the sheet and let moisture in.

Ask the roofer three things: whether they will broadcast matching granules into the bare areas or apply a coating the membrane maker approves, whether the reinforcement was exposed anywhere, and whether the repair keeps the manufacturer's guarantee valid. Get the answers in writing, with photos of the finished areas.