Laying pavers over concrete involves the same basic procedures as for laying pavers over dirt, but with a few extra considerations. You start by spreading a base layer of sand and then arranging your pavers on top. Sand is then also used to fill in the spaces between the pavers and set them into place. When laying pavers over concrete, you must also consider the edges of the space and create an immovable border to secure the perimeter of the area.
Before you begin, be sure to thoroughly sweep the concrete and remove any debris. You might also want to consider covering any cracks in the concrete with a weed barrier fabric to prevent vegetation from growing through your pavers. Once the concrete is clean and ready, spread a thin layer of paver base over the concrete. Paver base may be packaged as such, but is essentially fine sand that can also be called mason sand. This layer should be about 1 inch (2.54 cm) thick.
Create a perimeter about the width of one paver at the edge of the concrete by leaving it free of paver base. This perimeter will later be covered with mortar and used to create an immovable border. For traditional paver installation, you would dig a depression into the dirt for the area containing the pavers. In the traditional design, the higher ground around the pavers keeps them secure. If you are installing pavers over concrete, there is no natural support for the perimeter and the immovable border becomes essential for the stability of the pavers.
Once the paver base is spread, start in one corner and begin to lay the pavers in your desired pattern. After they are all put into place, remove the pavers from one edge and set them to the side. Mix just enough mortar for that side by following the manufacturer's directions. Spread a thin layer of mortar, working in small areas at a time, and replace the pavers according to your pattern. Repeat this process for the remaining edges and then allow the mortar to set according to the manufacturer's instructions.
Once the mortar is set, use a wide broom, such as a push broom, to spread polymeric sand over the top of the pavers. Be sure to push sand into all of the spaces between the pavers as you are spreading it. This sand will be what locks the pavers into place and provides for their flexible but stable joints. After the polymeric sand is pushed into all spaces and the excess has been swept off, spray the entire area with a fine mist of water. This will set the sand and complete your paver installation.
One extra consideration to keep in mind when laying pavers over concrete is the additional height that you will be adding to your existing concrete slab. If this slab intersects a doorway, gate, or other passageway, the increase in height could affect the function of that area. The pavers as well as the base below them add height and should be combined to determine the total increase in height. Make sure that your door or gate will still have enough clearance to function properly with this addition in height to the surface below it.