Clue: Sticky stuff, 21 down, doesn't make infernal paving? (4,10)
Answer: GOOD INTENTIONS
Explanation: Definition: infernal paving?
**GOO** ("sticky stuff") + ***(doesn't innit)** [anag:make] where INNIT is the answer to "21 down" 
*The road to hell ("infernal paving")is paved with GOOD INTENTIONS