I'm not so sure about that. I have always felt that the gm provides the moisture for the moss and lichen to grow. A totally clean roof dries super fast. A roof with even barely noticeable gm takes much longer to dry. Having said that moss and lichen seem to have different preferences. Moss definitely needs the moisture to get started.

A progressive study would have to be based on observed facts which would take a lot of time. Has my interest though.

I have a bunch of comp covered in gm from a reroof Im doing. I want to do a progressive study of different solutions for proof of our method. Could be illuminating. I would like it to be very comprehensive. If anyone has something they want me to try let me know. I plan on doing the study over an extended period of time and providing the results for all the members.

Dont mean to takeover the thread or anything, its closely related. I still plan on calling you for the pub run next time Im in Ireland Hickey.

Í hear you Eric about the moisture....That's why when I just see aroof with Moss or Just Lichen I am always amazed. This thread has now struck an intrest in me, to find the reason why...My investigation begins.