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3.3
3.3 Structure & Fabric :
metal, wood & Glass
water and detergent, then rinsing off with
warm water. Non-caustic degreasing agents
such as white spirit followed by clean swabs
can also be used.
Surface preparation
Paint should
be tested to determine whether it is lead-
based. If so, appropriate precautions
should be taken during its removal. It
may also be important to establish and
identify original paint layers, which can be
done through carefully taken scrapes.
Removing paint and rust from wrought
iron is best achieved by heating, which causes
the metal to expand and breaks down the
adhesion of the rust, allowing it to be removed
with a wire brush. This method does not affect
the mill scale – the outer surface of the iron
formed in the forge. Evidence suggests that
this is a protective surface and its removal
may accelerate decay (grit blasting of wrought
ironwork is therefore inappropriate). Heating
can cause thin wrought iron sections (less
than 2mm thick) to warp. Heat travelling
horizontally is a fire hazard and if the flame
is traversed too slowly, debris can become
fused to the surface. All these problems can
be avoided if the window is dismantled and
repaired in the workshop.
Other means of surface preparation
include acid pickling (off-site), preferably in
warm diluted phosphoric acid which forms
a protective layer of phosphates on the
metal surface, followed by thorough rinsing.
Cleaning with hand-held tools only removes
around 30 per cent of rust but is useful for in
situ work as a preparatory stage.
Priming
Once cleaned, the material must
be immediately protected from rust with an
appropriate primer or rust inhibitor, which
should delay the formation of rust for around
24 hours.
Assessment
It is now possible to fully
assess the extent of necessary repairs. This
may involve cutting out the corroded section
(often the bottom rail or associated jamb ends)
and welding in place a replacement section of
the same material and profile.
Repair
Welding wrought ironwork is
also best done in the forge because of the
laminated nature of the material. In situ gas
welding (brazing) or arc welding is possible,
but care should be taken that the welds extend
to the full depth of the material to ensure all
the laminated elements of the original are
connected, as surface welds have no strength.
Gas welding (brazing) is preferable as arc
welding requires the use of a non-corrodible
iron alloy wire or rod (mild steel is unsuitable
as it will corrode).
Wrought iron is available for restoration
work, primarily through the recycling of
old material. Sources of charcoal iron are
rather limited, but there are large quantities
of 19th century puddled iron available from
dismantled structures, which can be re-forged.
Repairs to both charcoal and puddled iron can
be made using reclaimed puddled iron as the
two materials are quite similar.
While mild steel has been used for
repairs to wrought iron, this is no longer
considered good practice, partly because
of the much greater susceptibility of steel
to corrosion. It is also well-established
that repairs are best carried out using
original material and techniques. This
is both possible and appropriate in the
case of wrought iron fenestration.
Painting
Because of wrought iron’s
natural corrosion-resistance it is sufficient
to protect it with primer and paint. When
choosing a protective paint system it is best
to consult a reputable manufacturer who can
advise on the compatibility of new and old
paints and on the best system for the given
conditions. Upgrading protection should be
achieved by increasing the number of coats
rather than using a more expensive system.
Two coats of primer and four coats of air-
drying paint should be adequate.
Dismantling and re-housing
Dismantling
and removing the sub-frame to a workshop
can disturb the surrounding masonry,
although historically fixings were usually
filled (or ‘caulked’) with molten lead. This can
be removed by heating the lead until it melts.
If dismantling is necessary, the frame should
be removed with minimum disturbance
to the housing and surrounding fabric.
Re-housing into masonry requires
abrasive cleaning to completely remove
all corrosion to fixing lugs prior to
painting with epoxy paints and fixing or
caulking with lead or lead wool packing.
Severely corroded lugs can be replaced
with new wrought iron sections.
STEEL WINDOW CONSERVATION
Steel window conservation began with the
listing of inter-war buildings in the 1970s
and 80s. The resultant demand has given
a tremendous boost to the steel window
industry, which has witnessed the emergence
of new manufacturers and suppliers in
recent years who have been instrumental
in establishing and implementing good
conservation practice.
After the introduction of the ‘universal
suites’ in 1918–20, most steel windows
were made of sections that had the same
technical specifications, regardless of
manufacturer. However, these original inter-
war sections are no longer in production so
splicing repairs, while technically possible,
are largely reliant on the availability of
salvaged windows of the period. Another
option is bespoke fabrication but this is
expensive. The adjustment of currently
produced sections is sometimes possible.
Produced before the introduction of
galvanising in the 1950s, inter-war steel
windows are prone to rust and their condition
depends on how well they have been
maintained. Rust is iron oxide formed by the
reaction of iron with water and oxygen. Left
unchecked, rust forming where paintwork
Factory-made steel casement window in the Arts and
Crafts tradition from a large house in East Sussex, c1895
(Brooking Collection)
Early 20th-century Crittall window from the 1904
alterations to Horton Priory House (1861), Monks Heath,
Kent (Brooking Collection)
Small top-hung light with vent panel in lower light made
by Henry Hope of Birmingham from the Midland Hotel,
Morecambe, c1932–33 (Brooking Collection)