Bricks, Masonry, Asphalt and Concrete - Concrete-look for fireplace surround and hearth?

I have been planning to reface my fireplace surround and hearth with slate tiles, but recently I've been thinking about how to achieve the look of decorative concrete without spending thousands of dollars on it. For example, something like http://www.buddyrhodes.com/studio/imageGallery.cfm ?

I had removed the old surround and had it built back up - it's cement block that's level and plumb with a pretty smooth surface - could I just mix up some cement and trowel it on? Is there a product that would work better? We have a wood burning insert, so it would have to be fire-rated.

Any ideas or advice are welcome. Thanks!