Tiling over cracks

I want to tile my back porch with some large glazed terra cotta tiles. The fllor is concrete but it has a few cracks in it. The edges of the cracks are level and seem to be stable. How can I make sure the tiles dont crack. I was thinking over covering th efloor in backer board and let that float on the concrete and put the tile on top of that. The porch is not covered, I guess you would call it a patio 14X28 ft.
Jimmie
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Use a crack isolation membrane. http://www.google.com/webhp?hl=en#hl=en&q=crack+isolation+tile
R
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Such as Schluter DITRA.
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