The most common tar application mistakes are using too much, coating damp or dirty surfaces, choosing the wrong kind of tar, and expecting a traditional finish to behave like modern paint.
Too much tar is the classic problem. A thick coat can stay sticky, collect dust, run in warm weather, and crack as it ages. Tar usually works better when it is brushed or rubbed into the surface in controlled layers. The finish should protect the material, not bury it.
Surface condition is just as important. Tar does not perform well on wet wood, frost, algae, loose paint, grease, or dust. It needs contact with the material. If the surface is not ready, more tar will not solve the problem; it will only attach to the weak layer and fail with it.
The final mistake is using the wrong tar for the object. Pine tar may suit wood, rope, and heritage craft, while road tar, roofing tar, coal tar products, and industrial coatings may be unsuitable for small craft, indoor objects, or handled surfaces. Match the material to the job and test before committing.