Modelling is often about learning new skills and techniques, recently I learnt something new - acrylic flexible filler.
The cafe is a cardboard kit from Stangel.pl, it was the first of the Dorfstrasse series of buildings and was the reason for purchasing more of the same. The interesting exterior finish was achieved using self-coloured flexible acrylic filler, see below.
Unfortunately, it does not seem to be available in the UK unless someone can provide an answer, until the only source seems to be Stangel.pl.
Try this YouTube video as a primer, the technique for applying the filler is the same as watercolour except the medium is a lot thicker.