Cast iron is the one metal where a general welder will usually make things worse. It is brittle, full of carbon, and it cracks if it is heated or cooled too quickly. Weld it like mild steel and a new crack appears next to the repair as it cools.
We repair cast iron properly — controlled pre-heat, the correct filler, and slow cooling so the metal is not shocked. It is a slow, deliberate job rather than a quick tack.
Machine parts and housings. Cracked gearbox cases, pump bodies, brackets and mounts, especially where the part is obsolete and cannot be replaced.
Stoves, fireplaces and grates. Cracked plates, broken grates and damaged doors on cast iron stoves and fireplaces.
Vintage and heritage castings. Old gates, railings, brackets and decorative ironwork where replacement would mean losing the original piece.
Pipes and fittings. Cast iron drainage and pipework components.
Cast iron holds far more carbon than steel, which makes it hard and brittle rather than ductile. When a weld cools rapidly, the zone right beside it hardens further and cannot flex – so the stress from cooling simply cracks it.
The fix is heat management. Pre-heating the whole casting before welding reduces the temperature difference across the part. Welding in short runs limits heat build-up. Then the piece is cooled slowly, sometimes over hours, so nothing is shocked. Skipping any of these steps is what causes the repair to fail.
Identifying the metal correctly matters too. Cast iron is regularly mistaken for mild steel, and the repair method is completely different. If you are not sure what you have, that is a normal question – we would rather establish it before starting.
Cast iron repair earns its cost when the part is expensive, obsolete or irreplaceable. A cracked housing on a working machine, a stove plate for a model no longer made, an original gate on an older property – in each case repair is cheaper than the alternative, or the only option at all.
Where a modern equivalent is cheap and available, replacement is often the more sensible route, and we will say so.
Cast iron work is better in the workshop where pre-heat and cooling can be controlled properly. Larger fixed items can be repaired in place when moving them is impractical — see on-site welding in Cape Town.
For background on the process, read what cast iron welding involves. For pricing generally, see our welding cost guide.
Unsure whether your item is cast iron? See how to tell cast iron from mild steel.
