Metal Window Restoration
Best Practice
Methods for Metal Window Restoration
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Survey and Catalog
Prior to our work each window was visually and manually assessed, photographed and a report with location and designation details uploaded to a management software called Zutec which was implemented by DBR London.
Each frame was also catalogued, photographed and steel tagged by Arts Heritage and a continual itemised progress report subcontractors and management team on site, enabling quick reporting and practical conservation. Our site team entered works data into tablets throughout the working day enabling real time coordination. This system was ultimately used by the conservation architects and project managers to sign off all works that had taken place.
Removal
Removal
The casements had been set into either a stone
or timber rebate. They were screwed into
position using steel screws into lead jackets or
directly into the timber.
Many of the screws had rusted through and
while around 30% of the original screws were
retracted either manually or by tapping and
reverse threading, the remainder were cut
through a 5mm opening in the putty. We
would go on to replace all the retaining screws
with stainless steel versions to avoid future
rusting.
Once free of retaining screws the putty
between the surround and casement was
manually stripped out using hammer and
chisel.
The frame was then carefully tapped free to the
external of the elevation and individiually
hoisted to ground level.
Cleaning & Stabilisation
Workshop Repairs and Replacments
Each window was assessed before cleaning and after to
mark damage and repair requirements. Where damaged
elements did not require replacing a combination of
methods were used to consolidate the frames.
The frames had been originally brazed, where this had
failed the elements were refinished and brazed once
again in the traditional manner. Where elements had
snapped or cracked, we employed modern welding
techniques including electric welding and also bronze
acetylene welding.
The surfaces were re finished using hand tools and light
abrasives. Some parts were missing entirely. New
components were manufactured to match and
incorporated. Some new windows needed to be
manufactured from scratch. To do this we disassembled
the required window. Mapped the components and
manufactured all the parts. The Windows were stamped
internally with the new manufacture date visible only if
removed.
Manufacture Replacement Parts
Almost every window casement was missing
some part or mechanism.
Where replication was required Master
Copies were manufactured to account for
shrinkage in the casting process.
These master sets were used to manufacture
the quantity required in both ferrous and
non-ferrous components. Each lever arm
was made up of 3 scastv iron components
and 4 cast brass components. Custom
washers and pins were also made to enable
the assembly of each part.
All components were manufactured using
the original and method employing
traditional skills in our foundries and
metalwork shops.
Repairs and Enabling Function
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Decoration
Workshop Stages Post Repair
1: Putty Removal - The frames were caked in a hard putty. One of the
longest stages of cleaning was manually removing this putty with hand
tools. It is not possible to shot blast putty from the surface as the shot
bounces off.
2: Paint Removal - The frames are hand sanded with dampened
paper and scraped free of paint. Operatives undertook those works
wearing powered respirators under full mains extraction to mitigate
possible lead contamination.
3: Surface Abrasion - Using a light shot of .08 & 1.2mm aluminium
shot the remainder surface paints, general debris and rust are cleaned
off. Aluminium is softer than the steel surface and was used so no
surface damage was made.
4: Inhibitors - A solution of tannic acid and ethanol was applied to all
ferrous surfaces. This is applied to prevent the future oxidation
process.
5: Primers - Two layers of Zinc Phosphate are applied. The first is
applied by brush and the second sprayed after drying. On low function-
complexity frames, a layer of micaceous oxide was added to the
external faces. We did not apply this coating to the internals as it would
limit the function of the catches and hinges.
6: Painting - Two layers of Dulux Metalshield Satin were applied.
Using a suitable and readily available paint is vital to ongoing
maintenance. It is for this reason that when dealing with large
quantities of functioning parts that we look to the future. While it is
possible to apply very specialist paint systems it is not practical to
Installation
The frames were set into a bed of new
heritage putty in their original rebate.
Even in their “type” The frames varied in
size wildly. Each frame would only fit into
its original position.
Once placed, stainless steel screws were
used to fix in and a sealing application of
heritage putty applied to the external
served to both secure the frame and make
it weather tight.
The top surface was then lightly abraded
by hand and a final application of top coat
paint applied by brush.