How to Make a Marble Slab out of Marble Window Seals

Wrap the exposed section of the window sill with two layers of heavy-duty paper. Secure the paper with masking tape. This will protect the surface of the windowsill. You need to be very careful during the removal process to ensure that the windowsill is not damaged. Marble is easily scratched and carved.

Cut the caulking around the windowsill with a utility knife. Angle the utility knife into the caulking, not into the windowsill. Apply only enough pressure to cut the caulk -- do not penetrate to the windowsill.

Position a pry bar under the windowsill, if the sill is on the interior of the building. Push the pry bar as far as you can between the wall and the windowsill, then push down on the pry bar carefully to crack the seal between the marble and the wall. If you are removing an exterior windowsill, point the end of a chisel into the crack between the marble and the supporting wall. Hammer gently into the adhesive or mortar that holds the marble to the windowsill. Keep the chisel almost horizontal so the point cannot damage the sill. Move the chisel from one side of the sill to the other as you chip away the mortar.

Pry or chisel until you loosen the windowsill. If you have an exterior sill, you will need to chisel the sides of the sill as well as the underside. Pull out the sill once you've broken the seal.

Lay the marble at your work station and remove the paper. Examine the marble for deep scratches. You cannot fill in the scratches with marble; you can only remove more marble to even the surface. You will have to grind down the surface of the marble to even it with the bottom of the deepest scratch.

Use diamond-grit paper and a hand grinder to even out the surface of the marble. Move the grinder over the entire surface of the marble to remove all polish, starting with 100-grit paper. This sanding process should also remove any caulking or small chunks of mortar still clinging to the surface of the marble.

Use a flat-head chisel and hammer to carefully remove large pieces of mortar. Do not angle the chisel too sharply or you will cut into the marble. Periodically check the surface of the slab with a level to ensure that you are not creating a sloped surface by concentrating on the areas around the scratches.

Switch to progressively finer grit paper as the scratches disappear and the surface of the marble becomes even. The finer grits have higher numbers. From 100 grit, switch to 200, followed by 400, then 800. Be sure to use the papers in this order, and to cover the entire surface of the marble.

Turn the marble over and repeat the grinding process on the other side.

Switch out the diamond-grit paper for a polishing disc on your hand grinder and polish the marble slab on both sides.