I have used copper naphthenate for about 15 years and I have never seen anything that lead me to believe there is any damage to the bees. I do dip the boxes in the fall and allow them to dry in storage over the winter before putting them in service. I know a number of beekeepers who use it on their boxes with good results, also.
AR I would like to ask you a general question. How much longer do you estimate that the life of the box will last treating as opposed to non diping? Thanks Phillip Hall
that`s a good question.
I guess, if you use a real "good" paint, they will last indefinitely if you redo it on a regular basis. of course the result is like a plastic box sort of. don`t know if the bees bother, I would.
As I do organic beekeeping, this is as natural as can be. So I use wood solely, often un-planed even. Most parts go untreated. They do fine for a VERY long time. Boxes that spend the winters outside I paint with raw linseed-oil. best to add some ground earth (pigments). also this has to be redone.
untreated boxes turn grey, they will do fine a long time.
most larger beekeepers I know don`t do anything with their boxes any more. Takes a lot of effort to paint or dip asf.
My pallets and screened bottoms are of larch-wood, untreated, which will last for many many years even if rained on.
all depends on the climate, of course.
to talk about the joints: if you paint "good" it doesn`t matter how the wood is fitted, as water won`t be able to enter anyway. So any "indoor" construction will work fine there.