Definitely rough. If the surface is smooth, Bondic may come off in one piece or chip off easily — that is because Bondic is not a glue. It contains adhesive properties, but for it to stick to smooth a surface, it needs surface tension instead of stickiness. If the liquid Bondic manages to get into cracks and crevices, it will hold extremely well. In other words, the rougher the surface, the better Bondic sticks!