How to Set a Marble Window Sill

Kasandra Rose

Most windowsills are made of wood because it is inexpensive and easy to cut. For a different look and a material that is more durable than wood, you can use stone. Granite and slate can work well for windowsills but for a high-end appearance, you might choose marble. Marble comes in several colors, with more unusual colors and patterns costing more. To save money, install the marble yourself. You will need some specialized equipment to cut the marble.

Marble patterns add the illusion of movement and flow to a flat surface.
  1. Create a template for cutting the marble out of the cardboard. Measure the windowsill width, the cutouts around the window casing and the depth of the sill. Transfer these measurements to the cardboard and draw the pattern of the sill. Cut the shape of the windowsill profile but leave the depth greater than needed until you have verified the cutout profiles are perfect.

  2. Lay the cardboard template in place on the window and make any adjustments necessary for a perfect fit. A small space between the tile and the window casing is acceptable; you will seal it later.

  3. Place the template on the back of the marble slab and mark your cuts.

  4. Mount the diamond cutting blade on the wet tile cutter according to the model's instructions. Fill the tray on the wet tile cutter with water to the fill line.

  5. Set the marble piece into the cutter to make the first cut on the edge that will fit into the window. Align the marble and slide the guides on the wet tile cutter into place; tighten the bolts on the guide to hold the tile in place. Cut less material than necessary rather that cutting too deep.

  6. Turn the saw on and slowly move it along the guide rail cutting through the marble tile. Approach turns carefully, just touching the cut line and then backing off. Turn off the saw and turn the marble tile to approach the next cut, resetting the guides to hold the tile in the new position.

  7. Use the tile pliers to snap off pieces that do not cut through cleanly. Break off stray pieces and interior corners until you've arrived at the desired shape. Test the marble in the sill position and make any adjustments before cutting the back of the marble tile to the desired depth. This is generally a straight cut, possibly cutting off the corners as well.

  8. Trowel on tile mastic and use the notched trowel to create grooves in the mastic. If the sill is not level, apply more mastic on the lower side to level the marble sill. Set the marble tile in place and check for level in two directions, along the sill and across the sill. Allow the marble tile to set overnight.

  9. Seal around the edges of the marble sill with caulk, smoothing the caulk line with a wet finger. Apply the high-gloss stone sealant, by the manufacturer's instructions, only along the edge not on the flat, top surface.