A slip component for a downhole tool has a bearing surface that is hard surface treated. The slip component, which can be a slip or other component of a slip mechanism used on a packer, bridge plug, or other downhole tool, is composed of a non-metallic base material, such as plastic, composite, or ceramic. To hard surface treat the slip component, at least the bearing surface is positioned relative to an ion sputtering apparatus. An intermediate layer is first bonded onto the bearing surface by ion sputtering an intermediate material onto the non-metallic base material of the slip component. Then, the bearing surface of the slip component is positioned relative to an electrosparking apparatus, which has an electrode composed of a selected external material for depositing on the slip component. Using the electrosparking apparatus, an external layer is bonded at least on the bearing surface.