Tar can interfere with paint by bleeding through, preventing adhesion, remaining soft underneath, or staining the painted surface.
Paint and tar are often poor neighbours unless the system is designed for it. Tar is oily, dark, and sometimes mobile. Paint may need a clean, stable, dry surface. If tar is soft, dusty, glossy, or contaminated, paint can struggle to bond.
Bleed-through is a common issue. Dark tar compounds can migrate into lighter coatings, leaving brown or black staining. Even if the paint covers at first, warmth or time may draw colour through the new layer.
Softness underneath can also cause failure. A hard paint film over a flexible tar layer may crack or peel as the tar moves with heat and weather. The paint may look successful until sun warms the surface or water reaches an edge.
Painting over tar is therefore a compatibility question. The exact tar, the age of the coating, the surface condition, and the paint system all matter. A general paint layer should not be expected to turn tar into a clean stable base by itself.