The expressed juices from the stinging nettle can be used to add a water resistant layer. This same juice in the past was rubbed into the small seams of leaky wooden tubs, which then coagulated and made the tub watertight again.
Although I have not tried it, I have been reliably informed that during the Second World War, French peasants, painted this juice onto old jacket made of Hessian, to produce what would now be looked as a cheap barber jacket.
Cronos