Waterfall foam is an expanding black foam used under waterfall spillway stones and boulders. The black expanding waterfall foam fills in the cracks and crevices of your waterfall so you have more water flow over your spillways for greater looking waterfalls. Use black expanding waterfall foam in streams and on edge treatments to help bond rocks together for more stability.  Black waterfall foam cures fast! Ready for water in 30 minutes! Much easier, faster, cleaner, and cheaper than using mortar or cement.