leveling floor when installing ceramic tile

I have a slab floor in an office area with the commercial type vinyl tile over it. The vinyl appears to be well installed and has no separations, etc. The problem is that the slab is not all that flat, and I was wondering if a mortarbed type install of ceramic tile might be a way to level it? It needs some type of new floor covering, regardless. If the vinyl was scuffed, could the mortar be applied over it? Thanks Bill
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I would not apply mortar over the vinyl. Your just asking for trouble
Find the high spot and then you can use an larger notched trowel for leveling of the new work. Do not try to use more than about a 1/4 to 3/8 of an inch. It will take a long time to dry. If you need more than that use floor leveling compound.
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This is stange. I would assume that the floor is at least smooth, and without any obvious ups and downs; otherwise, they would not be able to put vinyl tiles over it. Do you mean the floor has some holes on it?
Instead of eye-balling the floor to see if it is smooth, you may use a long string as a way to see if the floor is OK. That is the way to do this: - Have one person holding one end of the string and you hold the other end. - Get down on your knees and hold the string against the floor. - Move the string up and down to find the high spot along the string. - Use the string to sweep across the floor to examine all the area covered.
If you not only need to see if the floor is smooth but also need to see if it is level, you may need to do this: - Use a water level or something like that to establish a level line around the room. - Transfer that line down near the floor. - Again, use the string to examine the floor. But this time you hold the string at the level line near the floor.
Checking if the floor is both smooth and level is probably easier than just checking if the floor is smooth because you have the level line as the point of reference.

From my past experience, I found that I could put ceramic tiles over a floor that was not 100% level and smooth. But the slightly uneven floor introduced complication to the process considering the fact that I didn't have prior experience. Putting ceramic tiles over a level and smooth floor probably is easier than otherwise -- especially for a DIYer.
Jay Chan
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The slab doesn't have "holes", just sort of a 12+ foot "pattern" of poor quality strike and fill by the finishers. The "pattern" represents the striking boards used during the pour. Where the boards were, there is about a 1/2" high broad ridge compared to the center of the areas. If the slab was raw, you wouldn't see this, but with the glossy tile on it, the slab is obviously not flat. Ceramic tile would also show this "ridge" effect without some leveling. Laying the tile would not be a problem. I've put tile on much worse surfaces without problems (like rooms with heavy drainage slope), but I would do that only where visual conditions would not show contour problems.
Bill

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