Ballast is the rock used to hold real railroad ties in place. Our Ballast is great for modeling this effect and making gravel roads on your layout. It is available in several colors and sizes. Mix and match for a realistic effect. The product is lightweight and easy to use. Attach with Scenic Cement. Bags 18 cu. in. (Gray Blend 45 cu. in.)/Shaker 50 cu. in.