Beyond open porosity, pore size and morphology have been
shown to play a crucial role. However, their correlation to stainresistance does not represent a simple task and non-univocal conclusions
can be found in the literature. According to Dondi and
co-workers [9], stain resistance decreases with increasing the percentage
of coarse pores with an irregular internal microstructure.
On the other hand, Esposito et al. [8,14] argue that stain resistance
is strongly decreased by the presence of large amounts of small
pores from 1 to 10–15 lm[7,13]. In this regard, small pores are initially
less easily filled with staining agents. Nevertheless, it is
important to stress that once these pores are loaded by dirt they
can be very difficult to clean.