I saw a program this morning on HGTV that showed how to cover an existing concrete patio/steps with thin brick. They basically layed concrete down then the bricks over the existing surface. They then followed up with more concrete, filling in the 3/8" spacing between the bricks. They smoothed out the concrete between the brick using a standard brick grouting tool. It looked like a very easy job to do - the people on the show said the hardest part was moving the bricks to the job site. Concerning your adhesive on the concrete - I had the same on a porch. I used a sanding attachment to my drill and was able to "sand" off the adhesive very easily. Good Luck!