If this picture looks slightly different from the picture one post ago, it is because we took more material off the wall. When we tapped it with a hammer and it sounded hollow, we took it off the wall. No point in going to a lot of work and have the lime mortar fall off a few years down the road bringing a bunch of new material with it.
This is a completed windowsill that we just poured on the north wall. I regret to say I didn't take a picture of what it looked like before, so you will just have to use your imagination. Below is a picture of the form that I attached through the open window with the clamps I borrowed from Julian. The window is new, installed last summer, and Nancy still needs to add mortar around the edges to seal it up and improve the appearance. Before we added the window there was only a shutter to keep out the weather and the critters.