Installation guides

Installing window sills

Window sills are installed both indoors and outdoors. For exterior areas, a sill protects the plaster and masonry from rainwater. While its length varies with window size, its width is usually between 15 and 30 cm. The sill’s width must extend at least 3 cm beyond the wall so water doesn’t run down it. Sills can be made from any natural stone, though granite and marble varieties are most commonly used, since they have low porosity and absorb water more slowly. For the same water-absorption reasons, polished finishes are preferred over matte ones. Installing exterior sills must ensure a rainwater drainage slope of 5%. The exterior sill is fixed to the window frame at the points provided by the manufacturer, or alternatively recessed or fixed with dowels, with the fixing area then sealed. When bonding the sill to the window frame, avoid blocking the condensation drainage holes built into the frame.

Sill installation follows these steps:

• measure and prepare the substrate. Clean and mark it.

• cut a recess into the wall for the sill (recess depth is between 1.5 and 3 cm)

• mark the sill’s outline on the stone slab, based on the measurements taken

• cut the tile to shape using a circular saw with a diamond blade, then finish the edge

• place the sill in position, recess it into the wall, and protect the wall-to-sill junction with adhesive tape

• apply a layer of sealant at the sill-to-wall joint, spreading it along the joint. Remove the tape and clean off excess sealant.