Step 6: Place the Center Stones

Mark Powers placing the center stone in his pebble mosaic
Photo: Kolin Smith
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To make the mosaic sturdy, first bury the bottom third of the stones in the concrete mix. (Later, when all the stones are in place, you'll add a finer topping mix between the joints; see step 10.) Starting in the center, use a garden spade to dig a shallow hole in the damp concrete mix. Place the first stone on edge in the hole and pack concrete around it, holding it upright with your fingers.
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    Tools List

    • trenching spade
      Spade to dig out the base
    • 2x4
      2x4s to screed the concrete and hold a tarp in place as the mosaic dries
    • garden sprayer
      Garden sprayer or hose with fine-mist attachment
    • 2 nails and string
      Two large nails and string
    • garden spade
      Garden spade
    • 4x4s
      4x4 to set and level the stones. It should be about the length of the mosaic's radius so that you can work on one small section at a time.
    • mallet
      Rubber mallet
    • Natural Bristle Brush
      Paint brush to spread the topping mix.
    • mason's brush
      Stiff-bristled brush to shape and dress the topping mix.

    Shopping List

    1. Sand and scrap plywood to make a box in which to lay out the mosaic's design. (Or spread the sand on a plastic tarp.)

    2. Mosaic stones. Choose flat pebbles or cobbles in colors you like. We used green and slate black from the Signature Stones collection at Stone Decorative

    3. Paver base

    4. Stone dust

    5. Concrete mix, such as Quikrete.6. Topping mix. Also known as sand mix, it's finer than concrete mix and contains no aggregate. Quikrete and other companies make it. You'll add it like grout between the joints after laying the stones.

    7. Pavers, bricks, or bluestones to surround the mosaic and hold it in place.

    8. Plastic tarp or sheeting