Don't undermine the structure!

John has spent the last two days training members of Berkeley Group in Demolition & Asbestos Awareness from the client perspective.

During the course he has said, on more than one occasion, never undermine the structure when using a High Reach machine. So imagine his surprise when he got to his hotel to find that Rob Kulinski, a Twitter user known as @RobtheWrecker, had sent this piece of footage that perfectly sums up why you should never undermine the structure.