I have been lifting the floorboards in the upper balconies of an old chapel in order to inspect the joists, the timber plate in the wall (on which the joists sit) and the lath plaster ceiling fixed to the underside of the joists all of which are at least 130 years old. This has been a slow process which has meant clearing sack full’s of rubble from under the floor - bits of brick, slate, timber, rusty nails, discarded piles of lime mortar, dust and the odd fag packet. It would seem that builders were just as scruffy back then as they are today. Anyway, apart from one small section of wall plate, all of the timber which is old pine appears to be ok and the under joist lath plaster ceiling has a good key of lime plaster between the laths. My question is would it be prudent to treat all the timber with a modern preservative (Cuprinol 5 star or such like) before replacing the floor boards or should I just leave it alone?