Step 1: Dry Run
Put pavers together without adhesive to make sure the size and shape are what you want.
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Step 2: Glue Sides
Use landscape block adhesive to attach pavers. Run a thin bead of adhesive along the edges, press pavers together, then let sit for 24 hours. Clamps shouldn’t be needed.
Step 3: Attach Bottom
Glue the bottom piece on using the same method as for the sides. However, leave a few gaps between the adhesive beads so excess water can drain.
Step 4: Dry and Enjoy
Wait until glue dries completely, then add your favorite plants and enjoy!
SOURCE:http://www.bhg.com/gardening/container/plans-ideas/concrete-planters/