The pitted surface of the concrete throughout the estate is a deliberate architectural effect designed to emphasise the strength and monolithic quality of the material. Concrete for the buildings and the balustrades of the podium was all batched and mixed on site. Left as it was, the columns would seem to be made of rings, one on top of the other. The idea was to get rid of the horizontal joints between the successive sections of concrete by hammering the entire surface.
Originally the design of the exterior of the buildings involved polished concrete or ceramic material, Subsequently the architects changed their design of the exterior of the buildings to rough concrete. The use of crudely finished concrete had been championed by Le Corbusier. In one of his buildings, Maison Jaoul, Le Corbusier had used crude concrete barrel vaults combined with oak woodwork and rustic brickwork. Perhaps the architects included this building in their travels. Certainly the use of barrel-vaulted roofs for the terrace blocks is one of the most characteristic motifs of the Barbican.
A deep pick hammered finish was used on the outside of the buildings. You will see it in all the walls and columns. The architects first pioneered it in their earlier Golden Lane Estate development. It was quite successful. Columns do seem to be single monolithic structures. But if you look closely at some of them you can still perceive the different parts beneath the surface. A softer brush hammered texture is used inside buildings on stairs and landings.
The other reason for the pick hammering was to ensure that the granite-based concrete would weather to a uniform stone grey colour with the minimum of streaking. In their 1959 report the architects said: “We have therefore selected natural materials, the texture and colour of which stems from their nature so that some degree of weathering produces an acceptable patina rather than objectionable discolorization”. They weren’t quite so fortunate there.