Can Rockwool batts be pushed up against screws and nails?

A homeowner planning some retrofit work asked a building forum whether mineral wool insulation (sold under the brand Rockwool) can be installed in wall or ceiling cavities where nails or screws are sticking out into the space — a common situation in older garages or basements where fasteners protrude from framing. The concern was whether the insulation, which is stiffer than fiberglass batts, would still fit snugly around those obstructions or get damaged or pushed out of shape.

Two experienced builders answered that mineral wool handles this fine. Fasteners simply poke into the batt the same way they would with fiberglass, and installers likely won't notice much difference. For bigger obstructions, like odd chunks of wood framing, mineral wool needs to be notched and cut to fit around them rather than just squeezed into place, since it's less flexible than fiberglass. One builder recommends using a serrated "bread knife" style tool to cut it cleanly, including splitting batts to route around wiring.

Both builders actually prefer mineral wool over fiberglass for this kind of work. Because it holds its shape, it tends to fill a cavity evenly without much fussing, while fiberglass batts are more prone to compressing unevenly or leaving gaps if not installed carefully. For a homeowner considering mineral wool batts for a retrofit project with protruding nails or screws in the wall or joist cavities, this suggests the material can be worked into place without special preparation, as long as any larger obstructions get cut around rather than forced past.