If it wouldn't get a lot of traffic, I would use the GE Silicone II. I use it for everything & it's great!

Hi Tricia and welcome to GJ.

Not trying to run you off at all, but there is a mosaic forum over under the Homesite list if you want to check over there as well. Many of us post on both sites so someone who has a lot of experience with pebbles might see it here anyway. Then when you finish it, be sure to come back and show pictures.

I actually have the same question because I want do a pebble mosaic on my shed porch. So thanks for asking and I'll be watching the answers.

Hi Tricia~

Take a look at the this2that.com website...it's a website that tells you what kind of glue works best for certain mediums. Hope it will help you!

You want to look for Thinset. It's a cement based adhesive good for adhering stones or tiles. It comes in powder form and you mix it with water. You can get it at any home improvement store. The same workers who looked at you like you were nuts should know what it is. I had the same reaction when asking around for mosaic materials at a big box home improvement store.