Primer is used to enhence the adhesion of thermoplastic road marking paint and ground, play a role similar to double-sided adhesive tape. Primer is just used for the thermoplastic road marking paint, not used for the other road marking paints ( cold solvent, water-based, etc) .
For the clean asphalt pavement, the molten coating is applied to the road surface, the coating will be a high temperature to melt the surface of the asphalt pavement so that the two together, without the primer.
For the concrete pavement or old asphalt pavement, the molten coating and pavement can't closely together. So, In order to ensure the quality of road markings, you should buy a primer sprayer to spraying the primer on the pavement before you mark it with the thermoplastic paints.
By the way, DY-PS-II primer sprayer is not only used for spraying primer, but also for cleaning the road surface before marking. So, it's the best choise.