  Grain-grain processing has been shown to be an indispensable ingredient of
shock modelling in high density environments. For densities higher than
\sim10^5 cm-3, shattering becomes a self-enhanced process that imposes severe
chemical and dynamical consequences on the shock characteristics. Shattering is
accompanied by the vaporization of grains, which can directly release SiO to
the gas phase. Given that SiO rotational line radiation is used as a major
tracer of shocks in dense clouds, it is crucial to understand the influence of
vaporization on SiO line emission. We have developed a recipe for implementing
the effects of shattering and vaporization into a 2-fluid shock model,
resulting in a reduction of computation time by a factor \sim100 compared to a
multi-fluid modelling approach. This implementation was combined with an
LVG-based modelling of molecular line radiation transport. Using this model we
calculated grids of shock models to explore the consequences of different
dust-processing scenarios. Grain-grain processing is shown to have a strong
influence on C-type shocks for a broad range of magnetic fields: they become
hotter and thinner. The reduction in column density of shocked gas lowers the
intensity of molecular lines, at the same time as higher peak temperatures
increase the intensity of highly excited transitions compared to shocks without
grain-grain processing. For OH the net effect is an increase in line
intensities, while for CO and H2O it is the contrary. The intensity of H2
emission is decreased in low transitions and increased for highly excited
lines. For all molecules, the highly excited lines become sensitive to the
value of the magnetic field. Although vaporization increases the intensity of
SiO rotational lines, this effect is weakened by the reduced shock width. The
release of SiO early in the hot shock changes the excitation characteristics of
SiO radiation.
