If you didn't sign a paper contract, he's going to have a tough row to hoe in obtaining a mechanics (not mechanical) lien against your property. The old lawyer's joke is that a verbal contract is worth the paper it's printed on. I doubt he's going to hire a lawyer, because the lawyer will charge him $800 or more just to walk into court and absent a very narrow set of circumstances, he can't recover the fees he pays to his attorney.
From
http://consumerlawinvirginia.com/2011/09/25/when-are-attorney%E2%80%99s-fees-recoverable-in-litigation/:
In Virginia, the prevailing party in an action is not entitled to recover attorneys’ fees absent fraud, a specific statutory authority granting attorneys’ fees, or a contractual provision providing for such an award. This is the “American Plan,” every party pays her own lawyer.
He'll likely try and get you to sign something saying you owe him the money or get you to admit on the telephone that you agreed to having him do the work with him recording the conversation.
He may take you to small claims court, in which case you can't lie (since you're under oath) and say he didn't do the work, but you can provide evidence that the work done was shoddy and substandard. He'll also have to prove how much the job cost him, and if he subbed out the work and didn't keep any records, he can't prove how much he paid the sub.
Since he's not going to redo the work himself, I'd negotiate a settlement with him and have him sign a paper that he's giving up all future claims against you in exchange for the settlement. I'd start with his material costs and demand he show you reciepts for the material. If he didn't save them, tough shitski for him. Assume he used the cheapest paint he could and get an estimate on how much that paint would have cost him.
The point of negotiating a settlement is to make you both equally unhappy, which is always the sign of a sucessful mediation.