rfisher1968 and mm,
ah my fellow avs'ers... ...that would be a completely false assumption.
the light from your projector is definitely getting past those layers...
and the basecoat is definitely playing a roll in the contrast improvement.
i know this because i've done several rear projection screens using 5-6 duster coats a screen mix much more opaque than the one you listed. fact is, i could do 8-10 duster coats and plenty of light is still getting through.