I have a whole bunch of old 2x6s someone left in one of the barns. When I moved in the stack was about to the top of my head and I haven't used even half since then. Can I make a hive out of nearly all 2x6s? I was thinking if I need more width to just stack them side to side and have a 2x12" surface. If I did that would I need to seal where they touch?
You should be able to make a TBH entirely out of 2x6s. If you just get the crack between them reasonable tight the bees should seal it and glue it all together with propolis anyway. If the edges meet good and you want to glue it with a good grade of glue (I like titebond 3) the joint will be almost as strong (or stronger than) the wood. If
the wood meets. This kind of glue won't bridge gaps with much strength though.
If a TBH isn't simple and cheap to build it seems to me that the whole intent is defeated - don't go nuts with tongue and groove or biscuit joinery. I've noticed in the pictures that some of the most reputable bee keepers here use some pretty basic materials and techniques for their home brewed hives.
On the other hand I'm using half blind dovetails on MY