All gaps are then closed with either an Acrylic paste or plaster and one coat of Gesso is applied over everything to close the tiny unregularities of Styrodur

The sill was attached using a piece of Balsawood. I sanded out the slight hollow pattern. It was then coated with diluted Tamiya Putty. A first coat of very fine sand from the IKEA flower shop did not uniformly cover the different colors.