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You will need two and a half times the amount of batting as you need foam core. Then, get ready to layer your foam and batting. Make sure to apply an even, thin layer atop the wood base. Let it sit according to package directions. Apply an even layer, and then wait for it to dry. Lay and center a large piece of batting on the table. It will need to wrap around the base and foam to create the upholstered look. Center it on the table so that you will have more than enough batting on every side to wrap around the back of the base. Plug in the staple gun, as needed, and refill it with staples. Affix the batting to the base with staples within the first inch and a half of the edge of the base. Work from the center of each side out toward the corner. Use a hammer to knock loose staples into the wood. Create square corners by folding one side of the batting in toward the other side of the corner. Then, pull the batting up on the second side and affix it with several staples to the base. Make sure not to cut below the staple line.
Buy a large roll of batting from a craft store. Cut a piece of batting in the exact size of the foam core and plywood base. Set your wood base on top of the worktable. Glue the foam to the wood base using foam glue. Glue the batting to the top of the foam with a layer of foam glue. Pick your wood base, foam and batting off the table. Lay the wood base facing down on top of the sheet of batting. Choose a mechanical staple gun, an air compressor staple gun or an electric staple gun to affix the batting and fabric. Starting at the center of one side, fold the batting around the bench and onto the back of the base, pulling fairly hard to create tension. Staple every inch. Create round corners by pulling the batting around the center of the corner and affixing it right at the corner. Continue stapling until the entire edge of the batting is wrapped around the foam core and secured. Cut the excess batting from the bottom of the base.