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1 3 0 T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 1 6 T W E N T Y T H I R D E D I T I O N
3.4
STRUCTURE & FABR I C :
EXTERNAL WORKS
abrasive ‘blasting’ we are exposing the iron
in the same way as when it came out of the
mould after casting, although it is rarely
filled or sealed as effectively or as quickly. The
porosity of iron is a result of tiny gas bubbles
rising to the surface as the iron cools, leaving a
way in for moisture and allowing it to become
trapped under subsequent coatings. There are
many sophisticated and specialised modern
coatings for external use which are formulated
for use on steel which, unlike cast iron, does
not have any significant porosity issues. Many
coatings manufacturers see all ferrous metals
as the same, but the key is understanding
the complexities of the specific material in
question.
Surface preparation
Conservation projects of this nature are rare
so the team faced new challenges that resulted
in opportunities to develop solutions and
improve the process of metal conservation.
At the workshop each of the items, many of
which had stood saturated for years, was dry-
blast cleaned using crushed garnet, a natural
mineral widely used as a substitute for silica
sand in sand blasting. These components
were then placed in a low relative humidity
environment, in preparation for coating.
Some light gingering is to be expected due
to ambient moisture but it is easily removed.
However, in this case, black spots began
to erupt after a short time. The spots were
magnetite suspended in deoxygenated water
and because they reappeared after each
attempt to remove them, proper drying was
necessary. Items were placed in a custom-
made oven to dry over five hours after dry
blast cleaning. The worst affected pieces had
to be fired up to three times.
Temperature, humidity and timing
Many coatings manufacturers specify a
temperature range within which products
should be applied but they seldom refer to
humidity levels. Treating bare iron in an
uncontrolled environment during the British
winter has little chance of long-term success.
Unless humidity and temperature can be
controlled accurately, both in preparation
and application, modern coatings are
susceptible to failure. On the Grand Fountain
project small sections at a time were tightly
encapsulated using a proprietary system.
The area was blast-cleaned, warmed and
dehumidified to the optimum level, then
coated. Only in these circumstances will such
systems be effective for long periods.
Experimentation and application of
coatings, gilding and lacquer
Achieving the effect of Daniel Cottier’s
coloured glazes was perhaps the biggest
challenge. The colour scheme was based
on two main dark, rich colours: a deep
red-brown and a dark green. This was
lightened by bright, solid colour highlights,
gilding and overlaid glazes of bronzed
or gold-rich translucent varnishes. This
is achieved by adding bronze powder in
varying amounts to the first varnish mix.
The technique of applying bronze and
gold in powder form over wet varnish was a
skill developed by Lost Art and was varied
deliberately on repeat components. The
bronzing technique was used on various
elements of the fountain but particularly those
where reflected light would have an effect,
such as on the underside of the bowls. In this
case bronze and ‘gold’ dust was blown over
a varnished green paint coating repeatedly
until the effect was built up. To stay true to the
19th-century approach, no modern equipment
was used (other than a pair of healthy lungs).
Research showed that gold leaf had been
used to accentuate key parts of the structure.
To ensure the vision was re-created as
accurately as possible, the herons and the tulip
to the top of the structure are today finished
in the same way.
THE COATINGS
Following a test assembly of the fountain
in the workshop, the individual castings
were painted. Different parts of the
fountain required different coatings.
The pool floor plates, for example, were
primed with a 50/50 mix of zinc phosphate
and chlorinated rubber then coated
with 100 per cent chlorinated rubber to
ensure prolonged resistance to water.
The coating solution finally agreed upon
for the main body of the fountain was two
coats of zinc phosphate primer, one coat of
two-pack polyurethane (2 pk PU) undercoat,
two or more coats of 2 pk PU gloss and one
coat of 2 pk PU varnish, holding the gold or
bronze glazes as required, then a final coat of
clear 2 pk PU varnish.
This hardwearing coating system can
be removed if required and is therefore
‘reversible.’ However, it is vital that it keys well
to the (dried) iron and remains flexible during
expansion and contraction. This was why
such an expensive system was chosen over
epoxy paint systems, which are more rigid and
therefore arguably much less suitable for cast
iron.
TRANSPORT TO SITE AND REASSEMBLY
Great care was taken during packing
and transportation to the site to avoid
damage. The fountain was pre-assembled
in large sections in the workshop prior to
transport to site for final assembly. Soft
strops were used to tie the castings down
to minimise damage to the paintwork.
Castings were then checked on-site for
any damage and the final touches were hand
painted on site as part of the final assembly
process.
Original colours and protective coatings
were an intrinsic part of traditional cast iron
structures and can tell us much about the
technology and aesthetics of the era. It is
always worth investigating what lies beneath
modern, flaking paint – you never know what
you might find.
Further Information
Historic Scotland, Short Guide 4:
Maintenance and Repair Techniques for
Traditional Cast Iron, Edinburgh, 2013
cast-iron-short-guide.pdf)
AUTHORS: This article was written by Ali
Davey and Elaine Troup with the assistance
of James Mitchell of Industrial Heritage
Consulting Ltd and Daniel Lea, Production
Manager, Lost Art Limited. ALI DAVEY is
Project Manager, Historic Environment
Scotland ). ELAINE
TROUP is Regeneration and Conservation
Officer, Renfrewshire Council (elaine.troup@
renfrewshire.gov.uk)
Reassembly of the restored fountain