I am attempting to "repair" a bow with flax. It's still in the works but I treated the fine flax fibers like sinew. however, you need to 1) make the hide glue much thicker, 2) use a thick initial sizing coat before adding any plantfiber and 3) soak the fiber in water than in the glue before laying it down. If you don't soak it first, it will soak up the little glue on the exterior, taking in its moisture since it is so dry and preventing enough to remain outsid to glue it down. This is probably more important with finer processed plant fibers. Otherwise I treated it the same as sinew. However, I would say the hide glue did not provide any shrinking benefit like I hoped, like it does with sinew, so Iwould say just use titebond unless you want the option to remove the fibers for reuse.
