Natural fibre cordage can be preserved with tar by drying it first, applying a light coating, and keeping it ventilated so the fibres gain water resistance without being sealed into dampness.
Cordage made from hemp, flax, jute, manila, sisal, or other plant fibres can suffer when it stays damp. Tar gives the outside fibres a protective coating and slows water absorption. This is useful for garden ties, display rigging, rustic handles, historical craft, and outdoor lashings.
The cordage should be dry before treatment. If tar is rubbed into damp fibre, it can trap moisture and encourage the very decay it was meant to prevent. Apply a small amount at a time and work it along the strands. Thin cord needs very little tar compared with heavy rope.
After treatment, hang or lay the cordage where air can reach it. Do not pack fresh tarred cord into a closed box or bag. Once settled, it will still be darker, stiffer, and smellier than untreated fibre, which is useful for some projects and wrong for others.