This was my thinking in the other thread, and my meaning about "in" the concrete. Essentially soaking the sensitizer into the top layer. (Might not work.)

Quote Originally Posted by BrianShaw View Post
...sealant prior to coating could help also.
Actually I was thinking the other direction. Concrete is full of ferric compounds. If you're working with it green one generally works the dyes into the top few mm of the surface.

If a way can be found to exploit the ferric chemistry of concrete into a natural sensitized layer then it is part of the surface, not just sitting on top of the surface.

Of course, there is a real possibility that the other reactions going on to set the concrete would wreck any light sensitivity. But it sure sounds worth trying.