How to Fix a Crack in a Marble Window Sill

Marble, like granite, is a form of metamorphic limestone, and many assume a window sill made of marble is practically unbreakable. However, that is not the case. Marble is very porous, meaning it is full of microscopic holes. Unless the sills are cared for properly, they can crack without a great deal of force being applied. You can repair a marble window sill yourself, and you should seal it once a year with masonry sealer to extend its life.

Handheld electric router
Rags
Acetone
Two-part marble epoxy
Paper plate
Wooden craft sticks
Marble dust
Fine-grit sandpaper
Extra-fine-grit sandpaper

Instructions

- 1
  Rout very thin cracks using a hand-held electric router, because you need room to fill the marble crack with prepared epoxy. Clean all the areas of the crack thoroughly with a rag dampened with acetone.
- 2
  Transfer the two components of the epoxy to a paper plate. Place them side-by-side so they do not touch.
- 3
  Mix the two parts of the epoxy with a wooden popsicle-style craft stick. Add some marble dust the same color as the sill as you mix to tint the epoxy to match your marble. You usually can obtain marble dust from the same place you purchased your marble window sills or from most marble suppliers.
- 4
  Fill the crack with the prepared epoxy using the craft stick. Work the epoxy deep into the crack with the tip of the stick. Keep adding epoxy until it slightly overflows the crack.
- 5
  Smooth the epoxy surface with the flat part of the craft stick. Allow the epoxy to dry, undisturbed, for the amount of time specified by your particular brand of epoxy. This may vary from brand to brand.
- 6
  Sand the epoxy with fine-grit sandpaper to remove the excess from the surface of the marble. Wipe the marble window sill clean with a rag. Sand the area again with extra-fine-grit sandpaper to restore the marble shine to the surface. Wipe away sanding dust with the rag.

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