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Full Setts
 Method statements for laying full setts using SteinTec mortar.

Full Setts
What are full setts?
Full setts are those having depth not less than width.
For many ceturies the "golden rule" was that setts must be at least as deep as they are wide.  The heavier the traffic loading, the deeper the sett in relation to its width.  Before the advent of concrete and mortar, when jointing, bedding and supporting base were all unbound, this rule was very necessary.
Even with the development of high performance mortars and reinforced concrete for a base, we need to use full setts when the traffic loading exceeds a given maximum.
The deeper the sett in relation to its width, the more the strength of the pavement is taken by the joints between the setts.  So, with deep, full setts we can sometimes lay over an unbound or a bituminous base, even for heavy traffic.
British Standards BS7533-7 & BS7533-10 provide guidance for the specification of setts.
Non-Rigid Base
A non-rigid base can be made very stiff.
Consider a 200 mm DBM roadbase layer with a 50 pen binder.  Some texts would have us believe that this is as stiff as a concrete but a bituminously bound layer, such as a DBM, is fundamentally viscous and may deform over time or under fatigue loading.
An unbound aggregate layer can be constructed with a high stiffness but this also may deform over time or under fatigue loading.
When designing a carriageway or pavement, using full setts over a non-rigid base, the depth of the setts is crucially important.
The NBS clauses below may also be used for where a rigid base is present but the traffic loading is relatively light and the setts are small.
Rigid Base
A rigid base means a concrete base.
Concrete is both strong and stiff but it is also flexible.
Both shallow setts and slabs require a strong tensile connection with a concrete base in order to resist heavy traffic loads.
Full setts benefit from having a concrete base, much greater traffic loads can be supported, both from the increased stiffness provided by a concrete base but also from the creation of a strong tensile connection between the underside of the setts and the concrete.