MIG welding cast iron

Here at Feltwell Towers, the rainwater goods are showing their age. Most of the original guttering I've now replaced as it was beyond redemption, but generally the downpipes are OK and with a few repairs here and there they are good for a few years yet.

One exception was at the base of one pipe, where the original plinth offset bend had broken and was merrily chucking rainwater down the bottom of the wall. On removing this, it was stuck fast into the original rainwater "boot" - 100 years of corrosion would not be parted easily and whilst it eventually came away, the boot was cracked in the process.

A rainwater "shoe" - which many of you will have on the bottom of your downpipes - is a realtively common item that you can get new for about £30 + VAT. A "boot" is the same thing but longer (logically!) that you can now only seem to source from one place, the wonderful J & JW Longbottoms, but at some price - £155 by the time carriage and VAT have been paid. I can't use a shoe and any kind of extension piece, it would look a mess.

The horrific price got me thinking - for less than £150 you can buy a small gasless MIG welder, and I've read that it is possible to MIG weld cast iron. I could potentially repair the original boot for the same money, but have a small MIG welder afterwards. Strength here doesn't really matter - it's just to permanently seal the (very narrow, hairline) crack.

Anyone got any welding experience and care to comment? Online, this is the most relevant thing I could find.

http://www.mig-welding.co.uk/cast-iron.htm

If its not under any significant load I would be thinking about epoxy adhesives , fibre glass, chemical metal, to hold it together. Lead soldering would be the next up the list , then gas brazing. Stick welding with nickle rods might wor'k but won't be reliable under load , mig welding would be even more problematic and it would have to be a big (high Current) welder.

I'm sure you'll find another justification for buying a mig, that's if you ever need excuses for big boys toys.

Just re-read - "Strength here doesn't really matter - it's just to permanently seal the (very narrow, hairline) crack."

Welding it will make it more of a problem!

Sealent and / or paint to try and kep water out of the crack would be the way to go

My ancient ride-on mower had a broken cast-iron pully on the cutter deck and I asked an engineering friend about repairing it. He said it could be welded with the correct rods but that best results are obtained by first heating the item in a high-temperature oven for reasons I can't remember.

If the problem is just a hairline crack then welding may not be the best answer anyway. Wouldn't you need to grind a groove along the crack before filling it with the new weld? Otherwise, the weld would sit proud of the surface and be very noticeable. Grinding it back down would be pointless because you'd still have the crack in the original material.

If the aim is just to waterproof the crack then I'd agree with the above suggestion of epoxy resin.

That's not to say you shouldn't also 'invest' in a MIG welder. I may not use my one very often, but it's invaluable when I do.

Hmm. Epoxy or Chemical Metal would of course be much easier, I just doubted if it would be permanent enough. Soldering? Maybe, would it stick though? Then again, pragmatically, if the bottom of the crack leaks it will just drip into the drain. That articles seemed to reckon MIG brazing got the best results - but probably not for someone who has very limited, long ago experience of welding & brazing, and then not with MIG.

I would try one of the proprietary two pack metal repair resins, (Quicksteel comes to mind). I have used it to repair a fin on an old Villiers air-cooled engine and so far it's still intact. This would be preferable to welding and in a low stress situation would be almost as strong.
From experience cast iron is likely to crack along the weld line unless the stress is relieved from the weld.

Johnboy said:

From experience cast iron is likely to crack along the weld line unless the stress is relieved from the weld.

Click to expand...

I think that's the reason for my friend's suggestion about heating the item first before welding.

Actually, thinking about it a bit more, would a very narrow hairline crack in rainwater shoe/boot actually leak anyway? There will be no standing water and it would surely be more difficult for the water to find it's way through a hairline crack than just flow out of the shoe/boot in the first place.

As Feltwell says, what's the worst that can happen if an epoxy or similar fix should fail - a slight drip into the drain, along with all the other raindrops falling on the ground thereabouts. When the rain stops, the very slight dripping will stop and everything will dry out nicely.

You've persuaded me - as has a mig welding forum! I'd tried using an epoxy - JB Weld - on a cast iron component years ago, it failed fairly quickly. But, I've heard others swear by the stuff, so maybe it was my youthful rush to repair said part.

The worst that can happen here is that water gets into the crack, freezes and breaks the boot completely - in which case I'm not really any worse off than I am now. £150 for something so basic and utilitarian just seems too extravagant! Clearly my penny-pinching traits are coming more to the fore as I slide into middle age.........

I'll have to think of another excuse to treat myself to a new toy, I mean tool, now.........

Fair point about the water freezing risk, so you're only really needing something to waterproof the crack rather than do anything structural to hold it all together. I wonder if something a bit more elastic than epoxy would be a better idea? Perhaps epoxy would fail because of differential expansion as the shoe/boot heated and cooled? Although if Johnboy has successfully used such things on an aircooled engine then that would suggest a larger temperature range than anything a drainpipe would experience.

I have only used a gasless MIG once many years ago, but my results (on mild steel plate) were rubbish when compared to what I can achieve with a normal gassed welder. I have successfully managed to weld cast iron using a MIG with mild steel wire and BOC Argoshield as a gas. However, I was tack welding two bits together, and I think the chances of a seam weld right around a cast iron downpipe being OK would be small. I imagine that the stresses caused by the localised heat would probably cause more cracks, but that is just a guess as I've never tried it.
In your situation, I'd try an epoxy glue, and if possible something like a bit of Isopon P40 around the outside (or inside) to give extra support.
But, ... please don't let me talk you out of buying a MIG welder. I've had mine for years and it has been very useful on loads of occasions. I definitely suggest you get a gassed one though and not gassless, and also that you invest in a proper bottle of Argoshield or similar and don't just use the small disposable CO2 bottles. It seems to be available in smaller DIY sizes now, but I've not tried these. The small disposable ones do come with Argon and other gasses as well, but even then they seem to have a lower flow-rate or something else so they never work as well as the big ones.

I inherited a large (five foot tall) argon cylinder but it is now just about empty so I've been using the small CO2 gas bottles. They seem to work fine but they are somewhat expensive.

Once upon a time, it was possible to easily buy replacement gas cylinders but these days it seems you need to have an account and to pay rental for a gas cylinder, which is a bit over the top for my occasional use. I reckon a full argon cylinder would see me out, if only I could find somewhere to refill it or swap it for a full one.

Yep, if you MIG cast iron it will just crack again where the weld meets the cast. Welding cast iron and not having it fail again is tricky.

As this does not need to be structural, and the part is probably quite thin walled personally i would braze it. And it's a period repair method!

After cleaning paint/rust off use a christmas tree shaped carbide burr or delicate touch with an angle grinder using a thin disc to grind a vee along the crack. You only want to expose the base of the crack, removing as little material as possible. Cast iron is obviously very soft so this will be a breeze and cut beautifully.

Drill a hole at each end of the crack, this will stop it spreading and vee the hole so it is bowl shaped with your burr, or a file.

Yes you will need to pre-heat the piece before brazing, pre heating is absolutley essential. If it can fit in a domestic oven use it, and crank it right up though watch out for paint remnants smoking and catching fire. Of course you may have to send the wife out for the day to facilitate this. If you have a wood stove use it instead as that obviously gets much hotter than a domestic oven. Keeps the wife happy-er too. Keep an eye on it though, you don't want it glowing red!

With a good preheat you can probably braze it with a MAPP gas torch (readily available from any DIY shop). MAPP gives you a good bit more heat than propane alone which can make all the difference. If you are struggling to get it up to temp make a temporary forge to reflect the heat back into the workpiece.

Let it air cool naturally and then blend in the repair with a simple hand file. When it's done and painted it will be seamless and very strong.

If you have never brazed before, have a look on YouTube and decide whether you want to give it a go.

Or take it to a local blacksmith and ask them to braze it. I would expect at least £105 in change!

I agree that the plastic metal would probably be fine though if you prep it well. Not as much fun as brazing though.

BTW BOC are charging me £75 a year rental for a size X bottle of Argoshield which gives you an idea on where the break even point is vs disposables. You do need to open an account and sign up to an annual hire agreement & direct debit but anyone can walk in and do that. Just explain it is for hobby use. A size X bottle will last a hobbyist a very long time. I did 4 months of body repair on my old car and numerous other little jobs and there's still a good 1/4 left.

Yes the small bottles are not as effective as they are filled at a much lower pressure than a large bottle. The very high fill pressure (4000psi) and proper regulator on a large bottle gives you wide control over the flow rate, and an even flow. The regulators on the disposable bottles are not really proper regulators, more of a needle valve which is why getting a good flow can be tricky.

Not the most exciting of topics but I thought I'd post an update for anyone else considering similar patching up.

The boot looked fairly grotty.....



Cleaned up and crack ground out to a V, note air bubble in cast iron:-



Filled with JB Weld, filed back down again and painted - you'd never know it had been repaired. It looks super-glossy because the paint is wet, a final coat put on in-situ.



Please ignore the pointing - a job that I'm looking forward to so much I'm hoping to put it off for long enough to afford someone else to do it for me. I'll see how this repair fares over this winter, if it works I may just try an in-situ repair on a cracked S-bend I've got on another downpipe whose removal would require stripping a section of the roof and some leadwork - another easy one to keep putting off!

Good job. Thanks for posting an update - it's always interesting to know what has eventually been done after all the discussion.

Looking forward to a 'good news' post in springtime next year then.

I love a shiny black boot.*

never thought I would get to say that here

Lovely job Feltwell!

Super job, Feltwell.

I know this is now a superfluous PS to the thread, but I'm certain you made the right choice in not attempting to weld the iron. I did a bit of weldng as part of my engineering training, about 100 years ago, and the expert welder who trained me said that it took him ten years to learn how to weld cast iron. Even then, he said, he would never weld it electrically - only with oxy/acetylene.

Another thread prompted me to post a very, very long overdue update.....

7 years later and the JB Weld epoxy repair has held up just fine. Definitely the right way to go. But I had to treat myself to a MIG welder anyway :wink: :lol:

I remember a chap called Feltwell, but he was a much younger man.

NURSE! It’s alright, Penners is over here, you can stop panicking now, we won’t tell Matron you lost him.


Good to have you back Penners. Pull up a chair, have a KitKat old chap. Happy new year