When concrete has dried it is a dull, light grey colour. Some think that a concrete lintel exposed for its full depth on the external face of brick walls is not attractive. In the past it was for some years common practice to hide the concrete lintel behind a brick arch or brick lintel built over the opening externally.
A modification of the ordinary rectangular section lintel, known as a boot lintel, was often used to reduce the depth of the lintel exposed externally. Figure 93 is an illustration of a section through the head of an opening showing a boot lintel in position. The lintel is boot-shaped in section with the toe part showing externally. The toe is usually made 65 mm deep. The main body of the lintel is inside the wall where it does not show and it is this part of the lintel which does most of the work of supporting brickwork. Some think that the face of the brickwork looks best if the toe of the lintel finishes just 25 or 40 mm back from the external face of the wall, as in Fig. 94. The brickwork built on the toe of the lintel is usually B thick for openings up to 1.8 m wide. The 65 mm deep toe, if reinforced as shown, is capable of safely carrying the two or three courses of B thick brickwork over it. The brickwork above the top of the main part of the lintel bears mainly on it because the bricks are bonded. If the opening is wider than 1.8 m the main part of the lintel is sometimes made sufficiently thick to support most of the thickness of the wall over, as in Fig. 94.
The brickwork resting on the toe of the lintel is built with bricks cut in half. When the toe of the lintel projects beyond the face of the brickwork it should be weathered to throw rainwater out from the wall face and throated to prevent water running in along soffit or underside, as shown in Fig. 93.
When the external face of brickwork is in direct contact with concrete, as is the brickwork on the toe of these lintels, an efflorescence of salts is liable to appear on the face of the brickwork. This is caused by soluble salts in the concrete being withdrawn when the wall dries out after rain and being left on the face of the brickwork in the form of unsightly white dust. To prevent the salts forming, the faces of the lintel in direct contact with the external brickwork should be painted with bituminous paint as indicated in Fig. 93. The bearing at
ends where the boot lintel is bedded on the brick jambs should be of the same area as for ordinary lintels.