Plasticity models are frequently used to describe ceramic materials. Well established and often used ceramic models are those by Johnson and Holmquist. These are softening plasticity models for which mesh dependency is a well known problem. A viscosity or rate dependency can be added to the material model to provide regularization and solve the mesh dependency problems. For the Johnson-Holmquist models a viscosity is proposed to work on the hydrostatic tensile strength. A consistency visco-plastic formulation is used. For the Johnson-Holmquist-2 model it is demonstrated that the proposed viscosity indeed removes the mesh dependency problems. This is shown for both quasi-static and dynamic loading. In addition it is shown that the proposed viscosity can predict an experimentally measured rate dependent spall strength of alumina ceramic, while the original model fails to do so.