I've not seen anything like that before. Hard to imagine it would be insect feces because of where that spotting is seen - insect feces fall down, not sideways. It looks like the black spots are in small hollowed out concavities. Is that right? My guess would be termites.
1983 is fairly recent. I've never seen any construction product that would mark the wood in that manner. Could you shave off a piece of the marked wood and take it to Lowes or Home Depot (but make sure to get someone experienced in construction/renovations) and also to a pest control service in your town?
Wed 30 Oct, 2019 07:57 am
Looks like a severe cockroach infestation, try and locate any access points for the cockroaches and block them up really well, check for any leaks and fix them, use professional grade cockroach gel to eliminate any that may be hiding.