Question
I currently have bricks layed very nicely on a layer of compacted sand ontop of a concrete patio by a previous owner.  I have removed wood decking around the brick and would like to replace it with brick. In order to raise the new brick up to the level of the current brick I will need to put a layer of sand and compact and build a frame as a retainer.  It would be easier to scrape it all off and just lay all brick ontop of the concrete slab.  Is there anything preventing me from laying brick directly on the concrete slab or is it on the sand layer for a reason?

Answer
Without pealing it all back, or talking to the previous owner, its hard to say why the sand was used.  Maybe the concrete was cracked, or sloping the wrong way.  

If you are willing to go to the added effort, tearing it all out and starting over is a good thing.  Especially if you are adding MORE brick.  Then you can mix in the new brick with the old, and everything will match up better.  It is tough to match brick colors - especially if the older ones have been in for a while.  You can also change the pattern at this time, too, if you care to.

Once the old brick is lifted up, you'll have a better idea to see if just laying or mortaring the brick on top of the existing concrete is feasible.  

I would leave gaps between the brick and fill them in with sand, even if you do not mortar the brick directly to the slab.  I think it just looks better with gaps.

Here is what I mean: http://www.flickr.com/photos/bakermasonry/sets/72157601767110544/

Hope it helps.  ~M