grab adhesives

Inside but with a large weight cantilevered off it rather than just sheer.

 

That's clever.

 

I'm not so sure.
I had to remove some plywood recently that was stuck to some smooth bricks on a west-facing wall with no shelter.
It was stuck there in the late 80's with mastic, and it was still stuck on there very strongly.
Maybe the flexibility in mastic helped, or maybe the smoothness of the brick, but I'd have expected some modern adhesives to perform at least as well.

 

Pu foaming glue is the business for exterior use. Best to have some sort of mechanical fixing also though.