When Catherine is in the lab with Greg dissolving the film in the beaker of hot tea, her hand holding the tweezers change position in between shots.
Grissom states that when a body decomposes inside concrete it forms a vacuum that would be released when he and Nick use chisels to open the void where the body is found. But since her fingers were sticking out of the concrete form, the vacuum would be released when the flesh around her fingers decomposed and a gap was created for air to enter.
The wood concrete forms used for the house's foundation would have prevented the dead woman's fingers from sticking out the way they are shown. The fingers would have been easily visible to the construction workers when they removed the forms.
Luminol is moderately toxic, so the investigators would have been required to wear protective gear and evacuate everyone else prior to using it on the cement foundation.