Um, first of all, 'the work we done' is incorrect, grammatically speaking. It should be 'the work we did was hard' or “the work we had done was hard”. Second, and most obvious, 'hard' and 'tired' do not rhyme and never will, even with the Southern accent that makes it sounds really, really, really bad. Also, 'at night we'd sleep 'cause we were tired' doesn't make sense, because it implies that tiredness from their work is the only reason they sleep, even though sleep is natural. This song is screwed up.

I think Loretta Lynn is the only person in the world who can make 'hard' rhyme with 'tired'.