I've seen birch bark used to wrap (outside in) timber ends going into masonry walls in the national cathedral reconstruction project in Stockholm. The restoration carpenter I talked to said that that's how the old guys did it, and that the beam ends and masonry were the only things to survive the fire. He further asserted that there was little to no deterioration of the beam ends at the walls - dating from sometime before 1780.
That's fascinating. Makes perfect sense...