How to Color Concrete Block Marble

Wash the concrete block with soapy water and a scrub brush. If you encounter heavy grease or ground-in dirt, use a pressure washer and commercial degreasing product. Allow the concrete to dry completely.

Apply two coats of latex primer to the concrete surface with a paintbrush or roller. Allow each coat to dry completely.

Apply a coat of eggshell paint to the primed concrete with a brush or roller. Allow the paint to dry overnight.

Brush a thin coat of linseed oil on the painted surface to slow the drying time of future layers. This will give you more time to apply and blend the paint.

Mix a small amount of black paint into the eggshell color to produce a light gray. Apply this gray in random blobs over the surface.

Mix other concentrations of black and eggshell to make a range of gray shades. Again, paint onto the surface in random blobs. Leave areas of the unpainted eggshell color showing as well.

Brush the surface with a soft 3-inch paintbrush to begin blending and softening the paint. Brush in diagonal strokes to establish the direction of the marble.

Blot the surface with a clean rag to remove excess paint, then rebrush with a clean brush to soften the texture further.

Apply light veining to the surface in medium gray, using an artist's brush. This veining should be diagonal, following the direction of the marble, and shaped like bolts of electricity. The various veins can split and rejoin but not cross each other to form X shapes.

Soften the veins by brushing them with a clean paintbrush, following the diagonal direction.

Dip the pointed top of a goose feather into mineral spirits and shake off the excess. Hold the feather in your hand like a pencil and use it to draw delicate veins over the softened ones in a dark gray color. Redip the feather in mineral spirits frequently so you can draw delicate lines.

Soften these veins slightly by delicately brushing across them with a soft, thinner brush.

Allow the paint to dry completely.