cast iron welding

AFAIK, you need to get it HOT, not just hot. I assume that these are big grate-type things, in which case a little blow torch is not going to cut it. I believe that lack of heating the surrounding metal causes the weld to crack when the bead cools.

Also, are you sure they are cast iron and not wrought iron? Most gates, grilles etc. are (or were) wrought iron.

Tell them to get someone with the proper knowledge of welding cast iron to do the job. It's possible but needs skill so practice on scrap for a while before tackling. Definatley not MIG - gas or arc with special rods. It needs massive amount of pre heating and propane torch won't come anywhere near getting it hot enough for a large item. Even specialists aren't overjoyed about welding cast which gives you an idea what it's like.

Paul H

Is a while since I welded cast but here's what I remember.

You will need a MMA (stick weld) plant with the proper cast iron rods for the grade of iron you are welding. The rods can be expensive and the gases given off not nice so I'd also advise good ventilation and a face mask.

The weldability will depend on the grade and quality of the casting. A very poor (lots of pores and inclusions) casting will not weld well compared to a good casting with good grain structure. A higher carbon iron will weld well compared to a low carbon iron and a nodular iron is another matter....

To weld you will need to clean up the faces, remove any dirt or grease, deeply V the faces and then heat the whole area up until it is begining to glow. You will need to heat not just the weld, but at least a good few feet (or meter) around it as well.

The weld in small deep runs, removing all slag and other impurities. Once finished re-heat the iron and allow it to cool slowly or it may crack. Cast rods can be a mare to start and run, especially on poor iron so it it stops, clean the run and re start.


A far easier (and cheaper) alternative is to braize it. You'll have the strength and it's less hassle. As above, clean the ends, butt together heat until brass begins to vanish. Remember to heat a wider area as the braize will wick up the iron and add to the strength of the joint.

as mentioned above, braze it. its 100x easier than even attempting to weld it let alone getting successful results.

you rarley need a preheet with cast iron, the quality of the casting is more of an issue or if it has exotic properties. Some steel fillers can be used with some cast iron but they have to be for welding dissimilar steels. talk to a welding supply company and they will give you lots of advise but cast rods are very expensive . More important than a preheet is stoping post weld cracking so avoid draughts maybe cover with something after welding. After every pass chipp off the slag and pean the welds with the ball of a ball pean hammer to stress releave. Its not as bad as people say, buy a couple of rods and have a go. If it don't work , grind it out and try something else.
I've been welding steel , cast iron, aluminium and stainless steel for 24 years and nothings as hard as people will have you think.

she has got quotes from local welders in the area and they all want about 1500 euros per shutter and there a good 50 shutters on the ground floor (this chateu sleeps 30 people and is massive (chateau de bois giraud)

I've successfully welded cast iron with MIG. BUT, it does depend on the grade. I've welded cast iron heads successfully and a vintage cast iron garden roller, but had trouble with cast iron exhaust manifolds, but they did hold eventually when I turned the power right down. Doing a test piece is probably the only way to find out for sure.

I would say that 'iron' gates or shutters could actually be steel, unless they're very, very old. I was reading recently that most blacksmiths actually use steel because iron is too difficult to get hold of.

I pre-heated. I put it in the oven at top whack for about an hour to get it hot all the way through, welded it hot, and let it cool down slowly. If it's one join and you can't get it to weld, another workaround is to drill two holes and file a slot between them so you have a small dog bone shape. Fill it up with weld or braze to connect the two parts.