Sand down the glue after it hardens, using fine-grit sandpaper to polish the epoxy and blend it with the marble surface. If the marble counter repair involves putting two broken pieces together again, you should call a professional. In both instances, you’ll use small circular motions using it either by hand or an orbital sandpaper.

You want to be very careful not to sand through the gel coat and you probably won’t be able to remove a deep scratches or gouges. Cultured marble has a clear top coat called a "gel coat" just like fiberglass and it's purpose to protect the relatively porous marble from stains. So, if white is not a good match for your cultured marble, try your local marine supply store for an alternative.

Check for sill movement, such as a crack where one side has settled or is down farther than the other side, causing a crown and a crack. Apply the epoxy on top of the crack with a putty knife or the plastic applicator tool from the patch kit. Marble counter repair is simple, and in most cases you can simply buff out the crack as you would remove a scratch in the surface of a car. Mix marble dust that matches your countertop with polyester resin cement to form a thick paste that resembles the color of the countertop.

In both instances, you'll use small circular motions using it either by hand or an orbital sandpaper. I would probably start with 1000 or 1200 grit wet/dry paper which you can get at most auto parts stores.

Unfortunately, cultured marble tends to have swirls of color, so almost anything you use may not match the cultured marble exactly.




Source: homeguides.sfgate.com/fix-crack-marble-window-sill-39735.html
genaMarble
Sand down the glue after it hardens, using fine-grit sandpaper to polish the epoxy and blend it with the marble surface. If the marble counter repair involves putting two broken pieces together again, you should call a professional. In both instances, you'll use small circular motions...