Cast & Wrought Iron

Cast & Wrought Iron

Cast iron and wrought iron are frequently treated as interchangeable in general use. They are metallurgically distinct, and the difference determines whether a given repair method will succeed or cause further damage.

Wrought iron 

is a low-carbon iron, worked and shaped while hot. It is malleable and ductile — it deforms before it fractures. This working behavior is why traditional wrought iron gates, fences, and railings on older GTA properties were fabricated from it: the material could be shaped into detailed ornamental forms without cracking during fabrication.

Cast iron 

is a high-carbon iron, formed by pouring molten metal into a mold rather than working it while hot. It is hard and brittle — it fractures under stress or thermal shock rather than deforming. Cast iron is commonly found in structural bases, decorative newel posts, and older architectural components where a poured shape was more practical to produce than hand-forged work.

Repair implications:

Wrought iron generally responds to conventional welding repair in line with expectations for a ductile low-carbon material. Cast iron does not. Its high carbon content makes it prone to cracking under the localized heating of standard welding, which means the repair method has to be selected for the material, not just the visible damage. Applying a wrought-iron repair approach to a cast-iron component is a common cause of further, sometimes irreversible damage during an otherwise reasonable repair attempt.

A further identification issue: most iron-style fabricated work currently in place on GTA properties — including pieces referred to colloquially as "wrought iron" — is mild steel fabricated to resemble traditional ironwork, not iron at all. Confirming actual material composition is a required first step before repair, not an assumption to skip.