A tamped finish for unformed surfaces is produced by raising and lowering the compacting beam in its final pass to produce a surface with ridges at a fairly regular spacing of 20 to 30mm and up to 5mm high. Generally the grooves should be in the direction of drainage falls and on ramps (for example in car parks) should follow a chevron pattern. If the tamped finish is too heavy, it will impede drainage and lead to contaminants being trapped in the bottom of the grooves.
It should be noted that it is difficult to maintain an even distribution of ridges. In addition there will be variations from pour to pour, due to variations in the consistency of the concrete. Because of the lack of compaction in the ridges and the tendency for some residual bleed, this type finish can be dusty and may wear rapidly in heavily trafficked areas.
There is not a specification for a tamped finish or finishes in any British Standard or the Specification for Highway Works. However there is a brief mention in The Institution of Structural Engineers´ publication Design of Car Parks