Primer is a cleaning product, solvent or water based, used to prepare surfaces for bonding. The primer clears away any oil or mold released from parts. This process is critical for a good cement bond.
During a cementing operation, both surfaces to be bonded will be primed before the cement is applied. Between each application the shoe parts pass through a heat tunnel to quickly dry the primer. The primer must be matched to the material type. Rubber, EVA and leather each require a different primer.