About the making of lichens I cannot say anything.
The painting of the PU-foam...
When the foam was hard I started to cut rocks in it with a Stanley-knife.
I used the whole knife and not only a small part.
After lots of cuts in my hands and broken knifes I was content about the result.
Than I smeared Tile-glue (the stuff what is used to put tiles on a wall) on it.
I used a bit more water than usual so I could use a paintingbrush.
After this dried I repeated this a few times till I was content with the result.
Now I painted it with a waterbased paint that is used on walls.
When this was dry I repeated it till I was content with the result.
But to make it look like real rocks you have to do another paintjob.
I took the same paint and added a bit reddish paint so it became a bit darker. You can ofcourse use any colour.
With a brush where only a very small amount of darker paint on it I softly brushed the corners of each piece of "rock". Use only very few paint. The brush has to be allmost dry. This gives a 3D effect.