A dentil course is formed by projecting or recessing every alternate brick from the main wall face. Dentils are formed with headers with a projection or recess of a maximum of 28mm, although 18mm to 20mm is the norm. Dentil courses are more commonly formed using projections.
In one common application, a dentil course is sandwiched between two oversailing courses to form a decorative band; this is particularly effective at first-floor level on a house (see Fig 253). When constructed in this way, the resultant decorative feature is often referred to as a ‘string course’ and may be limited to an individual elevation or may extend all the way round the building. When building projecting string courses, the lower eye-line should be formed by lining in the bottom arris of the first oversailing course (as would be expected). The upper eye-line should be formed by lining in the top arris of the second oversailing course, which goes against the usual rule of thumb. Despite being above head height, the top arris is the most prominent edge in this case because the eye-line along the bottom edge is ‘softened’ by the presence of the dentil course. Again, the projections have been formed with Staffordshire Blue engineering bricks because of their high resistance to frost.
Projecting headers for a dentil course and other decorative features will lead to a corresponding recess on the back of the wall. This is of no consequence where the back of the wall is not seen. However, where the back is visible, a recess is undesirable, both from an aesthetic point of view and because it provides a ledge for rainwater to sit on. One solution is to cut or ‘snap’ the headers in half in order that one half can project forward on the front of the wall and the other half can be laid flush at the back. This type of application gives rise to the term ‘snap header’.