We use this special white granite material for some projects,which is not easy to deal with,not suitable for large area using and exterior cladding. It should be finished by Acid Cleaning first to clear away the black spots,and then use the Waterproof Additive to prevent against the spots' recur,but its nature is hard granite.More about this material,pls contact us: &Kevin Liu &Manager of export dept. &Kevin(at)xmyiyang.com &www.xmyiyang.com