[Cob] new earthen floor on old concrete floor

[Sabrina Free]

Hi,
Basically lurked here for going on 10 years, but have a question finally.
I rent a warehouse for my business, and am trying to make a somewhat
liveable area for myself, for the least amount of money possible.  My house
recently sold and until I decide where to live, am going to live here,
(albeit not exactly legally).
There are cement floors and randomly spaced plumbing, so have to work within
these parameters as I do not have the access to change the plumbing without
letting on to the landlord that I am living here.
The place where I need my laundry / kitchen / bathing area was used for
working on cars at one point, refinishing furniture another.  The cement
floor is horribly dirty and scrubbing 20 times has barely touched it.  I
still get dirt.  I could throw down a loose piece of vinyl floor to solve
the problem but figured it might be nice to get some natural building
practice in and kill two birds with one stone, so to speak.
So, am thinking to put an earthen floor on top of it and see what happens.
My question is this:
Does anyone have any ideas about whether or not the earthen floor will
actually bond with (or NEED to bond with) the concrete floor below?  Am
thinking grease on the concrete and a problem.  I can't put a nice sand /
gravel base down as I am only doing a small section of floor.  Besides being
dirty the concrete floor is pretty lumpy and uneven.
Also:
I don't necessarily want to do the entire warehouse, especially not at one
time.  Am thinking to do small sections, building a removeable frame to
enclose each section and then possibly expanding it to another section and
so on.

Thanks in advance,
Sabrina Free