How to Fix Cracked Marble Floors

Remove stain or paint from the marble floor surrounding the crack within a 2- to 3-inch perimeter. Apply paint remover on the floor with a paintbrush and leave it for five minutes so it strips the area of its finish. Wipe the paint-stripper from the floor with a clean rag. Rub a damp sponge over the area and pat it dry.

Rub a nylon brush over and around the crack to loosen flaking marble chips. Vacuum the area to collect dirt, debris and marble bits. Rub a tack cloth over the cracked area to remove dust.

Mix enough grout to cover the crack in a small plastic bucket. Pour a small amount of oil-based grout stain that matches the color of the marble or the veins running through the marble. Stir the grout stain with a stick.

Scoop some grout with a putty knife and insert it into the crack in the marble. Push the grout with the knife or your finger, and continue adding more grout into the crack until it is level with the surrounding marble surface. Keep pressing the grout as you insert it into the crack.

Remove excess grout from the marble surface with a damp sponge. Rub the surface with a lint-free cloth two hours after applying the grout. Leave the grout to dry overnight.

Inspect the dried grout for shrinkage and insert more grout into the crack, if necessary, until level with the surrounding marble surface. Allow the new layer of grout to dry for the time specified by the manufacturer.

Immerse a foam applicator in polyurethane and apply it over the repair patch to seal it. Allow the sealant 48 hours to dry before using the marble floor.