Featured Articles & Archives
Hoares Bank Restoration
Hoares Bank was founded in 1672 by Richard Hoare at the sign of the Golden Bottle
in Cheapside, London.
In 1690 he moved the business to new premises in Fleet Street, still within the
City of London. He continued trading at the sign of the Golden Bottle (a gilded
leather bottle that hung outside the shop). Street numbering was unknown in those
days and signs were used to distinguish one business from another.
C. Hoare & Co. is the sole survivor of the private deposit banks which were
established in the 17th and 18th centuries. As such it has a long and interesting
history, famous customers in the 19th century included Lord Byron; Jane Austen;
Lord Palmerston and The Earl of Liverpool.
In 1829 their premises in Fleet Street were rebuilt by Charles Parker and the
sign of the Golden Bottle was incorporated in to the design of the façade to maintain
the tradition.
The appearance of the Grade II* listed façade provides an important image for the Bank so when the original iron cramps used to tie the masonry façade together began to corrode and cause the stone to fracture, an ingenious discreet method of repair was required which also allowed the Bank to remain open at all times.
A typical construction detail in the early 1800s was to tie the stones together using iron straps known as ‘dog cramps’. The close proximity of the cramps to the face of the stone on the façade provided the ideal environment for them to corrode. As the cramps corroded they had the ability to expand between 7 - 12 times the size of the parent metal and this caused the stone to fracture.
The traditional method of repair would have involved the wholesale removal of the stone facing to locate the cramps and the replacement of them with stainless steel dog cramps with the reinstatement of the stone to match the original stone.
However, a more sympathetic remedy was required and the decision was taken early on by the clients technical advisors to locate the position of each of the dog cramps using x-ray mapping then install a cathodic protection system to prevent further corrosion of the cramps.
Corrosion is an electro-chemical process that involves the passage of electrical currents between anodic and cathodic sites with corrosion usually occurring at the anodic sites. An Impressed Current Cathodic Protection system involves the application of a low voltage direct current from an inert anode material onto the steel cramps to make all the cramps cathodic thus protecting them from further corrosion.
The first reported practical use of cathodic protection is generally credited to Sir Humphrey Davy in the 1820s. Davy’s advice was sought by the Royal Navy in investigating the corrosion of copper sheeting used for cladding the hulls of naval vessels. Davy found that he could preserve copper in seawater by the attachment of small quantities of iron, zinc or tin. The copper became, as Davy put it, “cathodically protected. The most rapid development of cathodic-protection was made in the United States of America and, by 1945, the method was well established to meet the requirements of the rapidly expanding oil and natural gas industry, which wanted to benefit from the advantages of using thin-walled steel pipes for underground transmission. This technology has been used extensively in the protection of steel framed masonry facades constructed in the early 1900s where the steel frame is relatively easy to locate and connect to.
Hoares Bank was the first successful use of the technology to arrest the corrosion
of isolated metal components (i.e not steel framed) embedded in a listed façade
of a commercial premises in the United Kingdom, where every dog cramp had to be
located and wired together with a titanium wire through a discreet hole in the
face of the stone (as photograph below).
An anode was then installed in close proximity to each cramp and the system was
completed once a low voltage direct current was placed through the system. The
whole system is computer controlled and is monitored remotely to ensure that it
performs efficiently.
Where the stone had already fractured and failed, stone was sourced which matched the original 1829 stone. This was then carved to match seamlessly and included a fine tooling pattern to the face of the stone.
The end result (as seen in photographs 4 & 5) is an effective method of corrosion protection to an important listed façade so discreet that all you see is the sign of the Golden Bottle as you walk by.
Robert Greer – Associate Director, Paye Stonework & Restoration
