Give the cement a few minutes , and then use your hands , a trowel , knife or any other instruments to add detail , smooth out certain areas and create natural rock contours . Again , reference real rocks to get it right . Place your rocks in a warm , dry place for around 5 days , with a light plastic cover over them . Every day , lightly mist the rocks and replace the plastic . This gives the rocks the best opportunity to cure properly – if they dry too quickly you might end up with cracks . After a few days of this , leave for another 24 hours to dry uncovered and then use a steel brush or sandpaper to smooth any rough edges that don ’ t look natural . Unless you added pigment in the beginning , you can now apply a concrete stain , being sure to keep it natural by making some areas slightly darker than others . Finally , apply stone or concrete sealer and allow to dry for another day before placing your rocks in your landscaping .