FLat and level are not he same thing.
It sounds like the slab is not level.
There are a number of slef leveling compounds that can be poured on the floor and allowed to set.
You have to create a dam so the liquid does not just run off the exising surface, but after that you mix, pour, and wait.
You could also use a thick mud bed to bring it back to level.

This would be about the same as using mortar to make the floor level.
You can leave it as is if you want. Tile needs a flat surface but not a level one.

Our house has a 30' x 20' family room that apparently had originally been a large open porch complete with sloping slab. The porch had been enclosed many years before we purchased the house but the floor had not been leveled. We had a concrete company in to do this about 10 years ago. If I remember correctly they poured 8 cubic yards of concrete from 0" to 5" deep. We gained a step from this room to our outside porch but it was great to no longer have a sloping room! We were initially concerned about the possibility of the slab cracking but we have no problems whatsover. I hope this helps.

Before you remove old vinyl or tile flooring, be aware that these materials frequently contained asbestos, and you can contaminate your whole house with an improper removal. You need to have this stuff tested at a local lab first, to determine whether you have a hazard or not. I've included a link so you can assess the situation better.

Here is a link that might be useful: Asbestos in flooring

sis3,

Did you remove the walls before the concrete was poured, or did the concrete just go flush against the walls?

Thanks...

The walls are frame construction and they were not removed. The concrete guys ran a laser line around the room to be sure of the correct level. Then they created 'shuttering' against the walls and concreted flush up to it. I don't remember any details of moisture barrier etc., I'm afraid, but I'm sure it was taken care of if needed.

"... 8 cubic yards of concrete from 0" to 5" deep"

How did they get concrete down to 0 inches?
The gravel content normally prevents this.

"How did they get concrete down to 0 inches?
The gravel content normally prevents this."

Whoops! I wondered about this myself when I typed it - My memory fails me, often! I will check with my resident expert (hubby) and report back.

DH reminds me that we actually raised the floor slightly at the high end (by about 1 1/2") and leveled the floor to about 5" at the low end. Just FYI a bonding agent was used between the old floor and the new concrete and fibers added to the mix for strength.
As far as errodr's problem is concerned perhaps there is no possibility of adding depth of concrete at the high end like we did. I don't know how deep you can make the self leveling material, my only experience of it has been for minor leveling.

Self leveling or mortar with fiber added.
It will hold up fine on interior use.
Most of the damage to cement products is from freeze-thaw cycles, and this will no longer be an issue for finished space.

I've had good luck using the products from this company when having to level uneven basement floor areas:
http://www.ardex.com/

Thickest I've had to go has been about 1 1/2".

But, first you have to get that tile off and heed the advice above regarding asbestos. Nasty stuff.

Once the tile is stripped the key to a successful pour is the prep. Be sure and use the prep Ardex recommends.

You can call the tech dept at the company and they will help you pick the proper product for your situation. It is a fairly easy diy project and the stuff can be skimmed to a nice feather edge.

g'luck

Ardex has great products, have used their K-15 many times, with excellent results. They are top of the line, that is the good news. The only down side is, they also are top of the line priced. But, you can't go wrong with them, as said above follow their directions and use the proper primer.

Paul