Just ordered wool roping/matting to use as sealer between the planks. It with the pine tar is what was used though they probably used various animal hairs depending on locale and what was available. Horse and reindeer come to mind as examples of horse rope/blankets have been found. Reindeer well again depending on locale may have been relatively prevalent? Finished a 3D design for a hewing broad axe that matches what we found in online resources. Sent it to blacksmith (JB Creations) to work on for us. This one is 1/4″ thick but will also ask for one 1/8>3/16 thick blade. Trying out 2 sizes for weight and ease of use just like we are doing with the mauls/sledge hammers.