Hi Peter, We have a new technology which will prevent the growth of moss and algae on all hard exterior surfaces, once applied to a clean dry vertical surface it will keep moss and algae at bay for 10 years, We have other new projects which we are prioritizing on so dont have the time to pursue this one at the moment, if you are interested and have the time to carry out some tests send me an email and i will send you on some samples. Regards Tadgh