If you plan on mortaring the pavers to the concrete, you don't need sand. If you're dry setting them, you need a layer of bedding sand.

Thanks. Would you recommend mortaring the pavers in or using sand?

My guys do it both ways. The advantages to sand are that it goes down quicker and you don't really have to worry about efflorescence from the mortar coming up through the stone. Mortar allows you to have whatever joints you may want (w/ sand, they're just butted up tight).

For my clients, I prefer mortar. If I was doing it myself for my yard, I'd do sand.

Thanks Marcinde! One more question I am hoping you can answer for me. I am laying a pattern with the travertine (consisting of 12x12, 6x12, and 6x6). As with tile, should I start in the center of the patio and work my way out? I see a lot of DIY articles where people simply start in one corner; however, they are not laying a pattern....

Thank you!
Jeff