Im am roughcasting an area tomorrow using k-rend, I have already bought the gear but am a bit concerned that I havent bought enough :-\ opinions on this 1 please it is an area 18ft long by 8 ft high with a standard door and a window that measures about 3ft sq . I have puchased a number of bags of reciever coat and a number of bags of roughcast dash . How many bags do you guys think I would need? Thanks