Tar and wax can both repel water, but wax may reduce tar adhesion if it is already on the surface, while tar can stain or soften waxy finishes.
Wax creates a water-resistant surface by filling texture and leaving a smooth hydrophobic film. Tar also repels water, but it relies on wetting and gripping the surface. If wax is already present, tar may have trouble reaching the wood, leather, or fibre beneath it.
A waxed surface can make tar bead, smear, or sit on top rather than bond. This is especially likely on polished wood, finished leather, or objects that have been repeatedly waxed. The tar may look dark at first, then rub off or peel because it never became part of the surface.
If tar is applied first and wax later, the result depends on how stable the tar is. Soft tar can stain wax and move through it. A hard weathered tar layer may accept some wax on the surface, but the combination can change sheen and dirt pickup.
The direct behaviour is that both materials resist water, but they do not automatically cooperate. Wax can block tar penetration, and tar can overwhelm wax with colour, smell, and softness.