The two frames are sewn together tightly with babiche. If you heat the bark with a torch it is easier to bend. A notched green stick is stuffed with birch bark and lit to provide fast intense heat. You hold it briefly close to the bark and it renders it supple. Two flattened sticks are tied together at the end to form a vise, squeezing the bark to the inside frame.
Surplus bark is trimmed away leaving a tounge of bark attached.
Step 13 Spruce tree roots are boiled and then stripped of bark and split. Soaked in water, they become a flexible sewing material. Once dry , they are hard and very strong, similar to rattan used on furniture. A small tongue of bark when folded down over, will makes the seam stronger and more water tight. Step 15 Spruce tree roots are used to sew the seams together.