I have been trying to use tree lichen for ivy for years now with various results. Most of the time it just looks like it is stuck on (because it is) and I have never been happy with the colors. I have a bag of lichen I have picked in my yard drying in different colors but it has been the application that has always defeated me.
I was looking at an old piece that I liked but was never entirely happy with.
I had torn most of the ivy off of it awhile ago and was looking at it today.
I liked the more organic look where it blended into the wall better.
I had some ruins I had made from leftover blocks from my gondor wall project and thought I would try a new method. I glued the lichen down before I had painted the walls, then did my usual spray paint, highlight, wash, highlight. This seemed to hold the lichen to the walls better. I think I'm liking the look of the greyness of the ivy vs color, looks older and more dead.
Some pictures.
Thanks for the tip!
If you try this, do so on a test piece first before you ruin your project you are working on! (voice of experience)