Scrub the brick down with soap and water, using a nylon brush to remove all the dust and grime. A clean brick takes paint more effectively than a dirty brick.
Allow the brick to dry completely.
Paint the brick with outdoor acrylic paint. Use a color that matches that of your home or paint designs on the brick, like stars, ladybugs or spirals.
Allow the paint to dry completely.
Spray the brick with spray varnish. Cover the brick with spray varnish by spraying first one side, allowing it to dry, and then spraying the other. At this point, the brick doorstop is ready to be used.