Hi Kruawun I suppose I'm an organic geochemist of sorts, in that I studying the effect that algae have on sandstones and other natural building stones. I'll be looking at the chemical as well as the physical damage it does, but I am only a couple of months into the study at the present time so I'm not actually sure what this will show. If you have any questions, I'll try my best! Ryan Welton ACM Centre Dept. of Civil, Structural and Environmental Engineering University of Paisley Paisley 0141 848 3288 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%