Yes, I've never seen or done this before.
Wing added to a mansion house in 1875 and on lifting floorboards off 8" x 2.5" joists found an intermediate layer between floorboards and lath and plaster ceiling below.
This layer consisted of tile batten nailed to sides of joists about 2,5" from the bottom, usual lathes between joists which have approximately 1.5" plaster with fine straw mixed in and a second layer on top of harder plaster approximately 3/4" deep. with a fairly smooth finish.
This leaves approximately 1" void below boards and as described earlier, about 2.5" void above ceiling.
So to be able to drill holes in the joists entails chasing out this layer,........... Easiest way I found is to use multicutter and accept their wear. Fortunately I can regrind them to get second and third life out of the blades.
Right, the question for you is why this construction? Fire protection or sound transmission or some other reason? I know the Victorian houses of this status with 1500+ acres did suffer catastrophic fires and were also very mindful of the servants listening in!
Regards
BOD
