Picture of Aluminium Casting Foundry
Making a foundry for melting aluminium (Aluminum for the US) out of a 13kg propane gas bottle

why am I making an instructable that many people have already done? well I thought it was an amazing Idea but I feel there was some room for better documentation, and a few little changes such as a lifting mechanism for the lid and no fire cement for the refractory.

Step 1: What you need

SAFETY NOTE: messing about with gas bottles or pressurized containers is very dangerous, do this at your own risk, but if you do decide to do it be safe, use your head, think about everything you do before you attempt to do anything. I have put in some tips as to what I have done in each step.

What you will need for this project

13kg gas bottle (UK), I got mine from freecycle.org from someone who didn't need it any more, in the US they are 12.4kg

Bag of sand

Fire clay

1.5 inch screws

a short length of steel pipe

nuts and bolts

a short length of hose


cotton wool


Angle Grinder with cutting discs and grinding discs

A file

Cordless drill and wire brush attachment

Arc Welder with 6013 rods (we find these rods easier to start and use with less sticking)

an outside tap

gas regulator if you're in the UK or you gas bottle doesn't have a tap

a steel rod if your gas bottle doesn't have a tap or you don't have a regulator


rags for cleaning

marker pen

extension lead for working outside



the bottle I'm using has the following dimensions

Propane: 13kg Patio Gas 580mm 315mm
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MichealF made it!2 months ago
I was brickies mortor to make the insulation. I may have made a mistake. Can anyone help? Perhaps I will need to start again. I am worried about it exploding! I also used an air compressor to push the air in. Perhaps this will lead to disaster also?
n1cod3mus (author)  MichealF2 months ago
the air compressor should be ok for the air, but the mortor might be an issue, concrete does have a tendency to explode when heated if there are air or water bubbles in it. I would redo the refractory if you can just for safety.
radarguy3 years ago
This is SUPER SUPER DANGEROUS! Please recommend against this. Unless you can remove the valve and flush the remaining gas out before grinding you have a potential bomb!

Although I would recommend against cutting it without flushing it out, it is not actually all that dangerous. I cut open an old propane tank a ways back and the sparks from the grinder ignited the propane. Instead of an explosion it simply made a whooshing sound as a blue flame jetted from the slot I had made with the grinder.

n1cod3mus (author)  radarguy3 years ago
which is what I did, flushed it out with water
blenz3 years ago
It is pretty funny reading all of the posts talking about how dangerous this all is. A couple of years ago the city had to change the supply tap from the main gas line to my house. Anything with these lines has to be welded, but they don't shut down the gas main. They drilled a hole into the main and lit it on fire until he was ready to weld in the new tap! For the old supply tap he did the same after he hammered in a steel plug! the entire time he was welding a 2 foot tall jet of flame was searing the cold February air. When it was all done he checked for leaks, you guessed it by playing his lit welding torch over all of the repair areas. So lets just all agree that "dangerous" is a relative term :)
enekuda blenz6 months ago
i worked a survey job on a main gass line running east west across the US and the pipe being several feet tall they were attaching a few foot tall pipe to that exactly how they did it, literally welded a pipe tap onto an active main gas line. its all in the techique and how safe and careful you are. needless to say there have been alot of deaths by normal people without training that cut into and welded to propane tanks and blew themselves up. just be incredibly careful
firesirt blenz3 years ago
If you think about it, you need oxygen for propane to burn, so it really isn't dangerous until it is well mixed with air.
n1cod3mus (author)  firesirt1 year ago
I believe the gas has to be around 7% compared to the amount of air for optimal ignition

Exactly. Which is why gas cylinders are so safe. There is an interesting mythbusters episode on this

The only real risk is that the additional heat from welding the tank could cause the tank to rupture (from increased pressure), and spill out gas fast enough for the flame jet to travel far enough from the container to damage stuff (like yourself). Generally, its really only dangerous if the burst of flame is unexpected.
n1cod3mus (author)  AJMansfield2 years ago
that couldnt happen as I drilled 2 holes in the top and emptied the gas out of it, by the time I came to welding it the top had been cut off.

the only time it would be an issue if the gas bottle was still sealed and i then started to heat it, your then looking as a pressure vessel which is dangerous, it would basically be a time bomb.
cfreitas made it!8 months ago

This is a great instrtuctable, and sorry for tooo late post, but I just want to say thankyou for this great y very well illustred instructions, N1cod3mus !!!!!!!

Some pics of my results :

n1cod3mus (author)  cfreitas8 months ago
n1cod3mus (author)  cfreitas8 months ago
nice furnace, glad my instructable helped, I am going to build a new one as I had to ditch mine when I moved house. I will be running the next one on propane I have made the burner already which there is an instructable for.
Nirgal383 years ago
Wonderfully detailed and well documented from beginning to end. That's the way all 'ibles should be.

Sadly, I lack the tools to build one myself but that doesn't mean I don't want one.

Incidentally, does anyone know where to easily find fire clay in the US? It doesn't seem to be an item carried by your average home improvement store (unless they have it listed under another name). I once built a forge from an old cast iron sink and have been interested in doing it again.
weldor Nirgal3810 months ago
Sodium silicate (aka to us old timers as 'water glass') and vermiculite mixed into a thick slurry. Slowly heat to 200 deg F. Tbe Sod. Sil turns to glass. If you drill holes and use a screw through the hole (secured by the nut) as an anchor point for stainless wire strung like a 'net' to help the slurry stay in place. You can use safety wire or mig wire. Stainless will not rot away and is quite resistant to heat as well
botnot Nirgal383 years ago
Look in Ceramics Monthly old editions (college library) for recipes. It is easy to make. Also refractory suppliers and ceramics stores will have it in stock. Not the low fire or 'artsy' stores, but a store that supplies clays and raw materials in bulk. look online or in the Yellow pages where you live.
Good luck,
(at random)
botnot botnot3 years ago
If unable to find fireclay, you can use Aluminum Oxide, [alumina]. It’s works really well. Sand blasting companies use Alumina and sometimes throw it away.

By the way, fire slowly at first. We 'candle', (very soft and low flame, sometimes overnight), until all of the H2O has dried out. Raid conversion to steam can burst off sections of the refractory, cause cracks, etc!!. We always fire slowly and progressively at first. The denser the castable, the slower we fire it. Most castables have the instructions on the package. Google is your friend!
Forgot to post that,
n1cod3mus (author)  Nirgal383 years ago
you could try pottery of ceramic suppliers, I got mine on ebay but im in the UK, if anyone else is in the UK clayman supplies do fireclay sometimes
weldor Nirgal383 years ago
Call a furnace or a boiler repair company. You may also find it at a local ceramics supply store.
IanQTBless10 months ago
After much research your instructable was the most detailed and well written. I've built a foundry in a similar style using a small oil drum instead of a gas tank, which is slightly larger. I used the same recipe for the refractory and in doing the curing fire a vertical crack has developed in one side (probably from drying it too quickly). It's a little less than an eighth of an inch thick, but runs a third of the inner height. Do you think it'll significantly affect the foundry?
n1cod3mus (author)  IanQTBless10 months ago
it will probably be ok, you could use some fire cement to plug it.
Kiwi 23 years ago
Very well written and you have made a good job of the little furnace.

I was very concerned though to read the description of how you began the modification of the gas cylinder. I am a former welding instructor having trained many apprentices and tradesmen over a number of years in NZ. I want to advise all instructable readers never to attempt to follow the same process to cut into a gas cylinder. Any attempt to modify an old cylinder in any way runs the risk of serious injury or death. I cannot stress this enough. There have been several incidents world wide where cylinders have exploded.

There is a much safer alternative for furnace bodies. I have made a number of successful furnaces and forges using the internal casing of old water heaters. These are about the same diameter of gas cylinders and are made from 3mm thick steel which can be cut very easily and completely safely using a cutting disc in an angle grinder. I have attached some photos.

Once again, a great instructable Chris but my advice is to never use old gas cylinders. You were very lucky.

n1cod3mus (author)  Kiwi 23 years ago
the gas bottle was empty, with no pressure, I drilled 2 holes using a battery operated drill, I would have used a manual hand drill if I had one, I did this slowly, then filled it with water to get rid of the gas which worked. no big bang.

I have to agree though if i could have got hold of an old boiler this would have been safer, but i was working with what I had.

It is not at all safe to drill holes even if you think there is no pressure. A minute amount of gas + plenty of oxygen + spark from drill bit = explosion. Filling totally with water means no oxygen = no explosion possible. Under any circumstance - unless somehow air can be trapped under the water, and the spark can reach it.

Which is almost EXACTLY the procedure used for industrial construction that is used before welding a tank like that. The only real difference is that they would leave the tank's walls intact, and use the tanks own valves instead.
n1cod3mus (author)  AJMansfield2 years ago
the valves on the UK tanks are one way and you need a regulator to use them, unlike the US tanks which seem to come with a tap attached.

I have to admit I was crapping my self while i drilled it but I made sure the valve was depressed while i was drilling so i know there wasnt any pressure and i used the drill really really slowly to try and prevent sparks, i guess you could also run water over the area being drilled to prevent sparks.
botnot Kiwi 23 years ago
Nice work! I spent a long time building offhand glassblowing equipment. 'Sometimes' the layer of glass on the inside of water heater casings can vitrify at higher temps and begin to degrade the castable lining from the back. INot to say that it will cause cause problems, but it can.
Great project, and thanks for sharing to all,
Calor-Gas1 year ago
Tampering with LPG cylinders or converting them to any other use as shown here is highly dangerous and can result in serious injury or death. Furthermore, Calor branded cylinders are, and always remain, Calor's property and as such, any conversion is unlawful and could result in Calor taking legal action or, if appropriate, in criminal prosecution. Please remove these photos, video, instructions and link to the Calor website from this site (and anywhere else it might appear online) immediately. Failure to do so may result in Calor taking legal action against you. Thank you in advance for your cooperation.
n1cod3mus (author)  Calor-Gas1 year ago
I will remove the link, but I'm not removing the photos, you can take me to court if you like. but the contract for that cylinder was with its original owner who gave it to me. I suggest you go find them ;-)
murban12 years ago
Here in the USA if you go to your local propane suppler and ask for a bottle that is no longer certifiable and tell them it is for a special project often they will often give it to you for nothing. Saves them the cost of having to dispose it.
Bald23 years ago
In the past I have had to repair by brazing the odd car gas tank. I think this dangerous operation can be made a lot safer by dropping a few chucks of dry-ice in the tank and leave one vent hole opened and let the CO2 purge bit before you start. With that in place my hand doesn't shake nearly as bad with the torch.
n1cod3mus (author)  Bald23 years ago
dry Ice is harder to come by in the UK
blenz n1cod3mus3 years ago
Really!? Why have they made it hard to find? (No criticism just plain curiosity :)
n1cod3mus (author)  blenz3 years ago
its not avaliable in supermarkets here, it would take a while to source it
blenz n1cod3mus3 years ago
I'm sorry to hear that, If I could I would ship you a whole carton of the stuff! Thanks for the 'ible by the way I hope I get a chance to try it this winter.
WareShoals3 years ago
Great instructable. For those of you looking for fire clay check out ebay: http://www.ebay.com/itm/Super-32-Refractory-Mortar-50-pound-container-/130470068688?pt=LH_DefaultDomain_0&hash=item1e609f41d0
I found some at the above address. WS
Thoth3 years ago
Couldn't you have used a wrench (spanner in the UK) just to remove the entire valve assembly, which would have made emptying out the gas much easier and safer?

Even running the drill slow there is a risk of explosion because the drill motor is constantly sparking.
weldor Thoth3 years ago
They are instaled with some sort of a locking sealer. I use my recipricating saw to cut off the valve. If you are concerned about the spark/gas thing turn a garden hose on the saw blade to basically seal the cut and you should be fine.
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