The Repair of Wrought and Cast Iron Work - Dublin City Council
The Repair of Wrought and Cast Iron Work - Dublin City Council
The Repair of Wrought and Cast Iron Work - Dublin City Council
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IRON THE REPAIR OF WROUGHT AND CAST IRONWORK<br />
BRAZE WELDING<br />
Brazing is a form <strong>of</strong> welding that uses an alloy rod,<br />
commonly brass or bronze, <strong>and</strong> is <strong>of</strong>ten the most<br />
successful method <strong>of</strong> welding cast iron. This is a<br />
specialist technique <strong>and</strong> should only be carried out by<br />
an experienced craftsperson.<br />
PINNING<br />
STRAP REPAIRS<br />
Strap repairs can be unsightly <strong>and</strong> their use is<br />
generally not recommended. However, they can be an<br />
effective short term, emergency measure to secure<br />
damaged ironwork until it can be correctly repaired.<br />
Straps should never be attached by drilling through<br />
the ironwork itself. Instead, two straps should<br />
‘s<strong>and</strong>wich’ the iron <strong>and</strong> be bolted to each other.<br />
Pinning is a particularly useful repair technique for<br />
cast iron that has fractured, although it may not be<br />
suitable for repairing structural elements. Fractured<br />
sections can be joined together by drilling one or<br />
more threaded holes into each fractured face <strong>and</strong><br />
screwing them together using a threaded stainless<br />
steel bar. <strong>The</strong> fractured faces should be painted prior<br />
to reassembly <strong>and</strong> the threaded bar coated in a layer<br />
<strong>of</strong> wet paint as it is screwed into place. Pinning may<br />
not be possible where the section is too narrow, in<br />
which case brazing may be a more practical<br />
alternative.<br />
STITCH REPAIRS<br />
Stitching involves drilling a series <strong>of</strong> holes along the<br />
length <strong>of</strong> the fracture <strong>and</strong> then drilling more holes<br />
perpendicular to the fracture. A series <strong>of</strong> metal ‘keys’ or<br />
stitches is then inserted into the holes across the<br />
fracture to hold the fractured sections together. <strong>The</strong><br />
advantage <strong>of</strong> such a repair is that it will allow much <strong>of</strong><br />
the original fabric to be retained <strong>and</strong> results in a selfdocumenting<br />
repair that will allow future owners to<br />
see where work has been undertaken. Additionally, it<br />
may be accepted as a structural repair by a structural<br />
engineer where a weld repair might not. However,<br />
there are drawbacks in that the fracture remains <strong>and</strong><br />
may act as a water trap <strong>and</strong> the visual appearance <strong>of</strong> a<br />
stitch repair may not always be acceptable.<br />
EPOXY REPAIRS<br />
Epoxy repairs involve the use <strong>of</strong> epoxy resin to build<br />
up sections or fill cavities <strong>and</strong> depressions in the iron.<br />
As with many repair techniques, the use <strong>of</strong> epoxy<br />
requires a compromise to the principle <strong>of</strong> like-for-like<br />
repairs. However, it is a reversible method <strong>of</strong> repair<br />
(epoxy can be blasted <strong>of</strong>f ironwork) <strong>and</strong> is useful for<br />
re-pr<strong>of</strong>iling corroded, pitted sections <strong>of</strong> ironwork so<br />
that they shed water, particularly where galvanic<br />
corrosion has occurred. An added advantage is that<br />
the epoxy will isolate dissimilar metals from one<br />
another where this type <strong>of</strong> corrosion has occurred. For<br />
a successful epoxy repair, the iron surface must be<br />
thoroughly clean <strong>and</strong> dry before application.<br />
Strap repairs can be visually intrusive <strong>and</strong> detract<br />
from the appearance <strong>of</strong> ironwork<br />
PLATE REPAIRS<br />
Plate repairs involve pinning a section <strong>of</strong> steel to<br />
ironwork. It can be a useful repair technique,<br />
particularly for fractured columns. In such cases a steel<br />
tube can be positioned within the hollow <strong>of</strong> the<br />
column <strong>and</strong> pinned through the column wall. <strong>The</strong><br />
disadvantage <strong>of</strong> this technique is that it is nonreversible<br />
<strong>and</strong> damages the historic fabric, due to the<br />
need to drill holes. <strong>The</strong>re is also a potential for galvanic<br />
corrosion unless the plate is isolated from the iron by<br />
an inert insulating material such as nylon. As with<br />
many other repair techniques, the merits <strong>of</strong> this repair<br />
need to be balanced against the potential loss <strong>of</strong>, or<br />
damage to, the historic fabric.<br />
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