I have seen in advice that you should place the core side outward on the outer board and the core side inward on the inner board to ensure they aim to bend towards each other and fit tightly. However, it is also the case that the unplaned side should be outward with the fibers facing downward, and if you go with this, you cannot fulfill the first rule unless you order special timber. What do you do?
.Yes, I thought so, primarily the rough side outwards. I was at the timber yard today, and it seems like there's no specific side that's planed, so you can actually pick 50-50 and get both rough side outwards and both heartwood outwards/inwards as I described earlier.