I really owe you a post, and there's liable to be a few inserted in retrospect. But in the meantime, here's a link to an article on shellacking-- in both its senses!-- that I just found on the BBC website:
"Who, What, Why: What Is a 'Shellacking'"?
Observe the paragraph on the use of construction terms to denote taking a severe beating. I wonder how that got started, hmmm?