I used celluclay elmers water and paint. Don't mix the celluclay much. Load up the four ingreadents before you start mixing, then try to leave it as "chunky" as possible while mixing. Spred it out like your runway needs to be and let it sit over night. Don't worry it won't dry. Nexxt day mix a darker wash (oh yeah, the paint is craft store acrylic- white) say a light cream, brush in depressions and all over. Use a real light grey for dark. Play with light & dark washes. You could also go to the pet store and get some coral or something close. Fish section. Haveing grown up in Miami, kicked around in the marines some that coral was not like white dirt. So they was and are "rolling" it often enough which gets the dust and small particles going. Otherwise knarlie, jagged, calicum rock, and you will see that underlay around the edges etc. Hope this helps.