Any idea what this coating on the wall is?

[Canyonrat2021]

Any idea what the grey oatmeal looking stuff is? It’s only on the walls where cabinets/closets were attached to the fiberglass wall. I’m assuming it’s some sort of adhesive but I’m curious if anyone knows specifically what it might be and suggestions for removing it. Some of it scrapes away fairly easily. But most of it is really on there.

Thanks for any suggestions you can throw out

[David Tilston]

When scraping glue, or what ever, off of fibreglass, I use a wire brush on a drill. If the stuff plugs up your brush, use a brush that is more corse.
If this is still a problem there are other style of brushes, like this one: