An element wall should give a monolithic impression when in use. There is to be a firm bond between the shells and the filling concrete. The bond achieved has an influence mainly on:
the load-bearing action, that is, the force transmissible in the joint (DIN EN 1992-1-1 very smooth to interlocked);
the composite action in terms of soundproofing (is a thick wall vibrating, or are three slabs vibrating);
the composite action in terms of tightness in water-impermeable structures.
For the structural approach, DIN EN 1992-1-1 specifies four options ranging from very smooth, smooth, rough to very rough. These options are illustrated in the image taken from Lenz und Zilch .
Rough is thus achieved by means of grains protruding by 3 mm (exposure), or by producing a basic roughness with a mean peak-to-valley height about the theoretical mean surface line of ± 1.5 mm.
The new DAfStb (Deutscher Ausschuss für Stahlbeton e.V. = German Committee for Reinforced Concrete) guideline “Wasserundurchlässige Bauwerke aus Beton” (Water-Impermeable Structures Made of Concrete) scheduled for publication at the end of 2017/ beginning of 2018 now adopts the requirement of “rough” according to DIN EN 1992-1-1, meaning that the required mean peak-to-valley height is increased from 0.9 mm to 1.5 mm.
The changes also include a new requirement to check and document the peak-to-valley height at the plant and to perform random visual checks on the construction site.