Hammered concrete finish

“The plain wall surfaces on the long terrace blocks above podium level will be faced with small-scale white marble blocks with riven faces. These have a light toned and lively appearance arising from the many irregular facets which also serve to break up the flow of rainwater over the surface and thus avoid the risk of street streaking or local discolouration.  … The columns above the podium, which support the residential blocks are of concrete, compounded of white spa aggregate in coloured cement matrix, polished to a fine surface. … The exposed edges of balcony floors, spandrels, plant panels and guardrails are faced with a small mosaic tile.”

Chamberlin, Powell & Bon, Architects “Barbican Redevelopment” April 1959

The pitted surface of the concrete throughout the estate is so obviously right, and emphasises the strength and monolithic quality of the columns and the concrete material.

But this was not intended from the start. What Chamberlin Powell and Bon really intended the buildings to look like is set out in the quote (above) taken from their final report to the City Corporation in 1959. You will see that the intended external finishes were to be small, white, marble blocks with irregular faces for the buildings and polished, coloured concrete for the columns.

Subsequently the architects changed their design of the exterior of the buildings to rough concrete. This was probably a decision pressed on them by the City Corporation to cut down cost and to make the construction work more efficient.

Chamberlin Powell and Bon may not have objected very hard. Pick hammered concrete did not have to be a compromise to them. They might even have preferred it. 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. Chamberlin Powell & Bon first pioneered the pick-hammering of concrete in their earlier Golden Lane Estate development for the City.

Concrete for the buildings and the balustrades of the podium was all batched, mixed and then poured in sections on site. In some columns you can see the rings indicating where one level of concrete was poured into a holding tube, set, and then a new load was poured on top. Left as it was, the columns would have looked roughly like bamboo.

But the aesthetic effect that the Corporation and the architects then employed was to hammer the set concrete all over with pick axes. The idea was to get rid of the horizontal joints between the successive sections of concrete by hammering the entire surface. As tiny chunks were knocked out, this gave what they called a ‘pick hammered’ effect.

The City Corporation and Chamberlin Powell and Bon experimented with various potential finishes before they settled for the pick hammering for exterior walls and columns, and bush hammering (a gentler effect) for some internal common parts where exposed concrete was to be used.  (Several of the contenders were created for inspection on a wall below Frobisher Crescent, where they can still be seen.)

The aim of the pick hammering was to take just enough of the surface concrete off to expose the bits of granite (the aggregate) below. But the workers had to be careful not to go too far or they would risk affecting the structural integrity (in the case of walls; maybe not so much in the case of columns).. The work couldn’t be done until the concrete was absolutely dry, so there was always a delay of 28 days between a wall being formed inside shattering (a box of three-quarter inch plywood in which it dried) and being lifted into place. Only when it was in place could the pick hammering be carried out.

Deep pick hammered finish was used on the columns and external walls of the buildings on the Barbican Estate above podium level, and some interior areas. It was also used on the massive boat edge balconies.

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.

One 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 discolouration. The choice of a limited variety of materials is aesthetically desirable in order to emphasise the contrast between different parts of the buildings.”

I think they have got away with that.