Sand the edges of your cabinets or other base for your countertop with fine-grit sandpaper. Make sure that all of the edges are level and not rough. Wipe down the base thoroughly with a damp cloth to remove dust and debris.
Squeeze a narrow bead of silicone adhesive or glue onto each edge of the base cabinets or other stand for your countertop.
Lift the new countertop. Hold it approximately 2 inches above the base and position it correctly.
Lower the new countertop gently onto the base on top of the glue. Install a pressure clamp at each corner of the countertop if it is made from a lightweight material to hold it securely to the base.
Wipe away any excess adhesive that escapes from the seams beneath the countertop, using a damp cloth. Allow the adhesive to dry for 24 hours. Remove the clamps, if used.
Sand the edges of the countertop base with fine-grit paper if needed to make them even and smooth.
Wipe the edges of the base with a damp cloth, if necessary.
Lift the new countertop and lay it into place atop the base. Position it correctly. Have someone hold it in place, if needed.
Sit on the floor and look up at the underside of the countertop. Find where the edges of the base meet the countertop and provide a good surface for screws.
Drill a screw every 4 to 5 inches along each edge of the base into the countertop, using a drill fitted with a screw bit. Use 1- or 2-inch screws, depending on the thickness of your countertop.