Re: The first 2" of bottom board
Painting the inside of a super is not needed the bees coat it anyway. A bottom board is best painted though, the paint helps protect the wood from absorbing stuff from all the rubbish that lands on it, specially stuff that's left to stew during winter.
There are paints available that are ecofriendly, it's not going to affect the health of the hive.
The landing strip I'll sometimes leave unpainted though, it gets washed by rain and I think the bees prefer landing on unpainted timber.
44 years, been commercial, outfits up to 4000 hives, now 120 hives and 200 nucs as a hobby, selling bees. T (mostly).