Problem: Every brick is unaffected by undulo.
Solution:
I believe this can be fixed by going into Options and increasing the FX graphics.
Problem: Doors, some windows, switches and buttons are unaffected by undulo.
Solution:
or not be trying to paint content bricks
Problem: It works on some bricks, but not others, some of them not being content bricks.
Solution: You can only spray raycasted bricks.