Blow-out grain sizes a_bo of grains consisting of an ice-mixture or porous silicate for different volume fractions of ice in the case ofice-mixtures and a vacuum in the case ofporous silicate, respectively (: compact silicate). The central star is chosen comparable to β Pic (see Sect. 2.4). The dashed horizontal red line represents the minimum grain size chosen in the simulations, smaller than any possible blow-out grain size a_bo within our model space: a_min = 2 μm.