Step 4: Position each bracket so it lines up with the marks on the wall, and mark holes for predrilling. Use a 1/8-inch bit to drill pilot holes into the wall. Attach the bracket to the wall with stainless-steel screws. (The exposed arm of the bracket will be hidden by the shelf.)

Use favorite flea-market finds as planters.

Step 5: Once the corbel is in place, use a level to ensure that it is plumb. Near the bottom of the corbel, where it tapers, drill a pilot hole at a 45-degree angle through the corbel and into the wall. Using a stainless-steel flat-head screw, secure the corbel to the wall. 

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Step 6: Lay out 2x2 or 2x3 boards for shelf material.  Make sure to allow an equal amount of overhang, not to exceed 3 inches, on either side. Space the boards evenly from the wall to the front edge of the corbels, leaving 1/2-to-1-inch gaps (for drainage) between boards. 

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Step 7: Mark and predrill the center of each board where it meets a corbel (avoid drilling into the brackets). Attach the shelf material to the top of the corbels with stainless-steel screws. Notch the piece of shelf material closest to the wall so it fits over the bracket and is flush with the other shelf pieces.