It sounds a lot better and feels more natural to say "Joe always puts a lot of salt on his food" You could also say "Joe always puts too much salt on his food". This would indicate that you think it is a bad thing and therefore it becomes more of an opinion. Saying " Joe always puts a lot of salt on his food" is more of a statement or it could be a fact.

You are right that it isn't normal to use 'much' in positive statements. 'Joe always puts much salt on his food' sounds awkward and unnatural. Informally, you could say: Joe always puts a lot of salt on his food. Joe always puts lots of salt on his food. Or rather more formally, you could say: Joe always puts a great deal of salt on his food. Joe always puts a large amount of salt on his food.