After you have finished admiring the wobbly bridge over the Thames you look up to the top of Tate Modern's tower, the chimney of the former Bankside power station. If you look carefully you suddenly get very disappointed. Because the brickwork is all over the place. Instead of rising in neat straight lines to the summit, the pattern of the perpends is like a child's early attempts to draw waves. So too, on the great panels interspersed by ranges of long slit windows which form the north, river-facing elevation - and probably wherever else there are large panels of brickwork.
Bankside Power Station is actually a modern building - but only in the sense that it was built between 1947 and 1960. Long before, in 1930, its architect Sir Giles Gilbert Scott had been brought in to redesign the exterior of Battersea Power Station and the result, a dramatically romantic form, was a triumph. Scott was subsequently to design a number of towered brick buildings including Cambridge University Library and Liverpool Anglican Cathedral. Oil-fired Bankside proved uneconomic following the world oil crisis in the 1970s and was closed down in late 1981 to sit brooding on the riverside directly opposite St Paul's Cathedral.
The original design had chimneys at each end but, following public criticism, Scott was able to persuade the engineers to combine the four flues into a single tower. As Ove Arup engineer John Hirst points out, the chimney is actually a brick windshield for the four flues.
The decorative bits in Bankside are vaguely Jazz Moderne, a bit Rotterdam School perhaps and nodding slightly in the direction of Frank Lloyd Wright. There's not a lot of decoration and it's incorporated into the functional details such as the mullions to the windows that break up the long walls with a brick version of Greek acroteria along the parapets. These and other details, at the tops and bottoms of fluting and around the shoulders of the chimney, often incorporate shaped lead flashing and standard bull-nosed bricks which Scott assembled visually with consummate skill and repeated over and over.
Given that the broad mass of the building was pretty much established these might, one suspects, have provided Scott with his most difficult design tasks. He was quite open about being interested only in the external form of his industrial buildings, establishing the elevations and working out what details were needed. After he had been paid a fee for his time he visited the construction only occasionally, leaving the main drawing work and supervision to the developer's own architectural staff.
The massive elevations of Bankside are not, as they appear, structural brickwork. They are, as you could expect with a post-war building, actually a brick skin. It is a slender one-and-ahalf brick (327mm) thick skin supported at 4.27m vertical intervals with horizontal steel beams spanning between the columns.
Behind the brick cladding at the base of the building there is mass concrete 9 or 10m high all around the building. The vertical strip windows have quite delicate brick mullions. Hirst thought he might have found an interesting case of reinforced brickwork, but it turned out that in every case the mullions are brick-cased steel members.
Hirst points out that in a brick and steelframe building of today the technology of hanging bricks on steel frames is well understood. Fifty years ago, it seems that the steel frame and the brickwork went up more or less together - with brick effectively wrapped around the steel skeleton of what are essentially combined stanchions and wind posts.
When Arups came to deal with the existing walls it soon became clear that although they were designed on the basis that the steel was taking all the stresses, in fact the brickwork was taking much of the load. And loads there were, for not only had the steel/brick combination to carry the normal building loads (and the special stresses of construction), it also had to cope with the fact that the mortar was hard post-war cement mortar. There were some quite serious cracks.
A great deal of the brickwork around the base of Tate Modern has been renewed. It is particularly obvious because Hertzog & de Meuron was anxious to retain as much of the tough industrial character of the building as possible: even the new gallery floors are unsanded oak and polished concrete. One of the consequences of this is that the architect refused to have the external brickwork cleaned. So although the new and old brick look quite different they are very similar under the skin.
The section of base removed round the cafeteria on the northwest corner was supported on a concrete beam created using the Pynford system. What happens is that sections of brick are taken out at intervals along the line of the new beam. Then Pynford stools, usually concrete, are inserted and bedded and reinforcing rods are threaded through them. The holes with their stools are then concreted up and when it has achieved adequate strength, the brick in between is taken out, the reinforcing bars linked up and the space then concreted up, the whole forming a continuous reinforced concrete beam.
The tower remains a free-standing brickclad steel frame. It was originally designed this way and the architect inserted two new vast brick panels either side to fill the gaps left by the demolition of the flue-gas washing plant which, until the Tate makeover, surrounded the base of the tower. Their perpends check out pretty straight.