Marble's decorative and generally durable nature makes it a prized stone for everything from statues to tabletops, but like other stone, it can break if dropped or a heavy object falls upon it. A broken slab of marble doesn't necessarily mean it's time to replace the object. As long as chunks aren't missing, the break is often repairable with a two-part epoxy or an adhesive designed for marble or stone.
A Thorough Cleaning
Before sticking the broken marble pieces back together, clean both parts thoroughly along the damaged edge. Brush the broken edges with a stiff nylon brush to remove loose marble particles. Wiping acetone along the breakage area will clean the marble, making it more receptive to the epoxy. Acetone, a key ingredient in nail polish remover, has a strong odor, so use it only outdoors or in a well-ventilated area.
A Clean Break
If the slab broke in a way that the pieces fit together nicely, with no gaps, a liquid epoxy or construction adhesive designed for stone can adhere the pieces back together. If you're using a two-part epoxy, mix the two ingredients together in a disposable cup, stirring the solution with a craft stick. Apply the epoxy to each broken surface, if the epoxy's directions recommend application on both surfaces, then press the slab pieces back together. Use a craft stick or disposable artist's brush to apply the epoxy. If any squirts out when you place the pieces together, wipe it immediately with a damp rag, following the line of damage to avoid getting epoxy elsewhere on the marble.
If the parts of the broken slab don't quite fit together, gather as much marble dust as you can or acquire some from a stone supplier, matching the color of the broken slab. Mix epoxy with an equal part of marble dust to create a color-matching filler for the areas missing chunks. Apply the epoxy to the broken area with a craft stick or artist's brush, then press the pieces together. Drizzle more epoxy filler into gaps and crevices to match the level of the original marble surface.
Holding It Together
While making the repair, use a clamp to keep the slab halves together, unless the break happened in a way that you could rest one broken chunk atop the other, aligning the slab vertically while the epoxy cures. If the broken slab is too big to use a standard wood or shop clamp, wrap a strap clamp around an area near the repair, but not directly over it, to avoid getting epoxy on the strap. Once the adhesive cures as recommended by the manufacturer, gently scrape away excess adhesive with a razor blade. Use a very fine sandpaper to smooth the repaired area.