Tarred canvas is made by treating suitable heavy natural fabric with a thin tar-based finish so it becomes darker, more water-resistant, and more rugged, while accepting smell, stiffness, and staining.
Tarred canvas belongs to traditional outdoor covers, bags, props, and maritime-looking craft. It is not the same as modern waterproof fabric. The treatment changes the cloth: it darkens it, stiffens it, adds smell, and can make it unsuitable for clothing, bedding, indoor upholstery, or anything that touches pale surfaces.
Use heavy natural canvas and test a small piece first. A thin tar-oil mixture or prepared dressing is easier to control than thick tar straight from a container. Work the finish into the cloth evenly and avoid saturated patches. The canvas should be treated enough to shed water better, not so heavily that it cracks, drips, or remains wet to the touch.
Drying and airing matter. Fresh tarred canvas should be hung or laid where air can reach both sides and where stains will not matter. It should not be folded tightly while still tacky. Once settled, it can suit covers, tool rolls, rustic bags, reenactment props, and outdoor decorative projects.