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 />
<strong>Wrought</strong> iron typically ‘delaminates’ as it corrodes,<br />
accentuating the fibrous structure <strong>of</strong> the material<br />
Galvanic corrosion is occurring between the original<br />
wrought iron gate frame <strong>and</strong> the metal <strong>of</strong> the filler<br />
rod that was used to form the weld joint attaching<br />
the gate catch to the gate frame<br />
<strong>The</strong> development <strong>of</strong> corrosion<br />
As the volume <strong>of</strong> rust is up to eight times greater than<br />
that <strong>of</strong> iron, even though a section <strong>of</strong> iron may appear<br />
at first glance to be completely corroded, it is possible<br />
that there is a significant amount <strong>of</strong> sound iron<br />
beneath the corrosion. However, developing corrosion<br />
material can exert great pressure on surrounding<br />
ironwork causing significant damage such as cracking,<br />
fractures, damage to surrounding masonry, <strong>and</strong><br />
eventual failure <strong>of</strong> the structure. As wrought iron<br />
corrodes it will <strong>of</strong>ten delaminate (the rust appears to<br />
develop in layers <strong>and</strong> takes on a fibrous appearance<br />
similar to wood). <strong>Cast</strong> iron corrosion tends to flake <strong>and</strong><br />
crumble rather than develop in exp<strong>and</strong>ing layers. <strong>The</strong><br />
force <strong>of</strong> exp<strong>and</strong>ing corrosion may cause wrought iron<br />
to bend <strong>and</strong> distort before it eventually breaks.<br />
However, cast iron is unable to accommodate the<br />
same degree <strong>of</strong> movement <strong>and</strong> is therefore more likely<br />
to fracture <strong>and</strong> fail without warning where exp<strong>and</strong>ing<br />
corrosion exerts pressure.<br />
Where rust forms a continuous, unbroken <strong>and</strong> <strong>of</strong>ten<br />
glossy layer on the surface <strong>of</strong> ironwork, it can in fact<br />
act as a protective barrier. This is commonly seen on<br />
wrought iron h<strong>and</strong>rails that have a smooth sheen on<br />
their surface. But where rust develops <strong>and</strong> exp<strong>and</strong>s in<br />
flaking, laminated layers it causes real damage. It acts<br />
as a moisture trap, which in turn accelerates the<br />
formation <strong>of</strong> more rust.<br />
Mechanical action<br />
<strong>The</strong> most common types <strong>of</strong> mechanical deterioration<br />
are caused by unstable or settling foundations <strong>and</strong><br />
impact damage. Unstable foundations, corrosion <strong>of</strong><br />
the base in which iron elements are anchored, or the<br />
settling <strong>of</strong> ground beneath ironwork can all cause<br />
instability, fracturing <strong>and</strong> deterioration <strong>of</strong> the<br />
ironwork.<br />
Impact damage caused for example by v<strong>and</strong>alism or<br />
cars, can cause deformation (in the case <strong>of</strong> wrought<br />
iron) <strong>and</strong> fracturing or shattering (in the case <strong>of</strong> cast<br />
iron)<br />
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