Sills are fixed on the outside of window ledge. This forms the weathering part of opening. It protects the building fabric below the window opening. When rain falls on the window, it drips down and lies on the ledge when the sill is not fixed. This can eventually cause dampness to the wall below. This also may allow water to seep through causing efflorescence. Another issue can be having rain tears appearing on the building facade below the window.
Window sills can be in built during construction or after the building. There are different types of sills in the market. This may include, clay, concrete, stone or wood. Each type has its own advantages and preference is on the home owner to choose the desired variety. When using the in situ ones, they should be protected until the finishes stage is complete. The wood ones are used in the dry areas due to the vulnerability of weather.
The clay or concrete sills are usually fixed after the window frame is in place. All sills should be done with an overhang or projection from the wall. This should be minimum two or three inches from the wall. They should also have a fall to ensure water and dirt flows away. They should be about one inch in thickness. It is important to ensure that they are place about half an inch above the bottom frame. This will allow the sash to open without touching them.
The fixing of sills starts with measuring the projection and window recess into the wall. This is measured from outside. The window ledge is then made level. The first and last sill is then bedded on strong mortar. A string and spirit level is used to align the top and and overhang distance. It is important to recess them two inches into the wall on both ends. The rest are then bedded on the mortar and space filled out. Below the sills mortar is filled to make good the space. A matching sill color can be painted to have a uniform decoration.
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