He won't stop licking the kitchen floors

I wish I did.  All of mine do that....floors, furniture, etc.  Drives us nuts and we are constantly telling them to "leave it".

Is there a reason why this is a problem, other than that its annoying? If that's it, might I suggest you keep the floors clean of anything harmful, and ignore it?

If he's licking constantly, it could be an obsessive behavior which can be very difficult to overcome.  Correcting obsessive behaviors is never going to work. 

ETA:  here's an article that may be helpful if this dog is displaying OCD  behavior.  Please note that corrections are not only not going to change the behavior, they can make it worse. 

http://www.whole-dog-journal.com/issues/13_9/features/Dogs-With-OCD_20062-1.html

 what Jackie said.

I have a "stop licking" command that my dogs know. They aren't particularly OCD but Neiko licks an area on his front leg when he is stressed and Lily licks/bites on her feet due to allergies. The stop licking was more of a redirection in the beginning (not a correction), now they will stop licking whenever I saw the words and I don't need to redirect them. 

 Make sure you are only using soap and water to clean, nothing that will be harmful to them, while you work this out (or adjust to it).  I have not ideas re the licking directly, sorry.

Do you maybe use a scented cleaner - I know there are a lot out there and maybe that's why they are licking it (other than an ACD behavior).  It does sound like OCD though.

I use hot water and vinegar to clean my floors and it does a great job.  And not at all harmful or toxic - I use the same white vinegar I cook with.  Even some soaps shouldn't be digested.  I made the switch when we had our daughter and I cringed at her crawling around amongst chemicals on the floor.

 I would (in this order):

1. Make sure to use something non-scented, non-toxic to clean the floor.

2. Take him to the vet and rule out any possible medical reasons (deficient in some vitamin?  Weird seizure activity causing the behavior?).

3. Maybe have him wear a cone/e-collar so he cannot lick the floor and in the mean time, work out a combination of more exercise and giving him alternative things to do (chew a marrow bone, use a food-dispensing toy).

4. Possibly consult with a veterinary behaviorist if it appears to be more of an OCD type behavior than just being bored or liking the taste of the floor.

My first thought, as someone else mentioned, is that he likes the taste of something you may be cleaning the floor with.  Is he licking in the same spot all the time or at random places on the floor?  Perhaps something was spilled in a particular spot previously and he's trying to find more?  Although I'm absolutely and 100% NOT an authority (on anything!), I have discovered that most of the time there is a reason for what they do.  Might be a bit strange to us, but they have their reason.  The trick is getting to their reason. 
Example:  My dog started licking his paws incessantly not long ago.  Driving me crazy.  In the meantime, I am covered in chigger bites from the grass outside my apartment.  (apartment, hence I can't do anything about it)  Anyway, it occurred to me yesterday...if I'm scratching like a lunatic from chiggers, he may well have chiggers between his toes.  He can't scratch his toes so he just licks.  I put a bucket of water next to door and started cleaning/drying his feet before we come inside.  The jury is still out, but it *seems* to have made a bit of a difference.
PS:  I really like/appreciate the idea of cleaning floors with vinegar.  Had not thought of that and certainly cheaper than floor cleansers.  Thank you! - Susan