Now it’s time to test the foundry, or at least the first version of it. This also has a benefit to it. Some others who have made this style of foundry have found this process helps the concrete to fully cure, and dry any leftover water still in the mixture. This process is pretty simple, most suggest using charcoal as the main fuel. We went down the local hardware store and they had a sale on charcoal briquettes. These are small and there are plenty of them, and fit nicely in the foundry. Light the fire in any way you are used to, we used fire lighters and some cheap kindling, also from the hardware store. If you don’t know how to light fires safely, find somebody who does.
We didn’t use much to start with, this is meant to be a calm fire to help cure the concrete, and test it can deal with at least some hot temperatures. It was also to see how well it burnt with the air hole we put in. Main problems we found were that the air hole did not provide enough oxygen into the system, so the fire was slightly stinted. We tried blowing into the hole a few times, and the fire definitely got bigger, but it also sprayed ash into the air, so be very careful of that. We also noticed something most blogs talk about, lots of heat escapes from the top. With the foundry having such a big opening, very little of the heat is retained, and the fire has to work harder to keep the heat at a set level. A lid is often the best way to battle this.
So what have we learnt from our first fire? We need a lid, and some way to force air into the hole. This will be a topic of further posts, but for now we know our concrete foundry can withstand the heat of a fire, and is now a little bit darker from all the ash. Thanks for reading, and hope to come with another update soon.
At this point we had a cast foundry base, made out of sand and plaster of paris. To see how that was made, see the tutorial here. Before we first test it though, we had to make one modification, and that was to drill a 30mm diameter hole in the side of it.
The idea of the hole is to allow air to come in and fuel the fire. The theory goes that the air comes in the side, and the resultant fumes (like smoke) leave via the opening at the top. It makes sense because heat rises, and takes all those hot resultant gasses up with it. Note that we don’t really care about the fumes coming off the fire at this point, we just want as much oxygen as possible to get to the coals. If hot exhaust fumes are leaving via the same hole as the oxygen, but going the opposite direction, they will interact with each other, slow each other down, and make the furnace much more inefficient.
Also notice the hole is angled down into the base of the furnace. This isn’t by accident, we want that hole to do two things, pump air into the base of the fire, and not let anything go back up the hole. This hole in the future may contain a fan, to pump more air in. We don’t want the embers flying back up the pipe and breaking the fan during use.
To drill the hole we used a hammer drill bought from Aldi, and a 30mm masonry drill bit, these parts can be pretty cheap if you search around, and the hole doesn’t have to be this exact size. Use what you can find, and make sure you get help when doing the drilling. As always, safety is important, and safety glasses and gloves would be a good idea. if one person steadies the foundry, while the other drills, it is much easier. Go slow, so that the plaster on the inside doesn’t break too much. It is easy to be too eager and create large cracks and chips, which could mean an entire restart.
Although this was a shorter post, the next one will be about the first tests! As always, thanks for reading, and I hope to be along with another update soon. If you guys have any tips, questions, or want to show your foundry, please post in the comments below.
So we had our aim, and a basic design based off we saw in the videos we had watched. Now we needed to start the process of making it. We made a list of materials we might need, and had a basic look around on the internet, and off we went to the shops. During our travels we visited Screwfix, Wickes, B&Q, Hobbycraft and even Homebase. There were some pretty simple things we needed. Listed below:
Plaster of Paris
Drill (and drill bits)
smaller plastic bucket
cheap measuring jug
Some of these items you might already own, (and we did) but it was listed as things we needed to complete this stage of the project.
Safety Notice (don’t ignore)
At this point I am going to stress a couple of those boring safety points. We have worked with some materials that could be considered quite dangerous if improperly used. So use safety gloves wherever possible (these can be as cheap as £1.50 in some stores, so there is no excuse!) and goggles and masks are a good idea, especially with dust, and when drilling. If you don’t understand why these are needed, maybe you should stop reading at this point.
We would recommend thinking about where you do this project, there is the potential for spillage of plaster of paris, and that can ruin surfaces; so kitchens are probably out of the question. We recommend outside on a nice sunny day. Its always a good idea to be in a nice open area with plenty of ventilation, even when not working with toxic chemicals, it’s just good practice. We chose out outbuilding, its airy, already has paint stains, and contains all the tools we need as it doubles up as a basic workshop.
So let’s get on to the bit you care about how we made the foundry. The method starts with mixing together a mixture of 3.5 parts plaster of paris, 3.5 parts sand, and 2.5 parts water. This can be scaled up or down depending on how much you need to make to fill your bucket. We used a standard 14 litre bucket, and a standard liquid measuring jug to mix parts.
A few good tips to add in at this point. You should probably get some friends for this project, a few extra hands can be really useful. while we were making ours, we had one person stirring the mix, and another adding in the parts. Notice below, how many hands are in the images. The other point is to add the sand and plaster of paris before the water. As soon as the water is added, the mix will start the process of setting and you need to get that stuff mixed as fast as possible before it gets too hard. The last point is to mix this a lot, you want it to be thoroughly mixed together, else it could separate in the drying process.
Also, it would be a good idea to wear gloves at this point in the making, plaster of paris can cause burns if it gets in contact with the skin. Read the packaging first, and be careful when handling the powder and the mix.
While the mix is almost at its fully ready state, somebody needs to get the smaller plastic bucket, and fill it mostly with water. The amount of water used will depend on your buckets and mix. The water makes it much easier to hold the smaller bucket in place while the main mixture sets. If you get it right, it should not need much force to keep it in place until sufficiently hard.
Once it is held in place for around 5 minutes it should be hard enough to let go of. if not, it may need to be held longer. You could always put heavy items on top to keep it in place. After a while it should look like the one below. Able to be left without touching, slowly drying.
Remember that at this stage, it still needs to be left for a long time before we actually take the bucket out, preferably for 24 hours, but it will depend on the mix you made, your climate, the temperature, all manner of things. We recommend leaving it overnight. When you touch the top of the mix, if it is moving then it isn’t ready yet.
The next stage is very fragile though. First empty all the water out of the inner bucket. Then we used a pair of pliers to slowly move the sides of the bucket away from the newly set mix. The bucket was slightly damaged, but with patience it is possible to remove the inner bucket to leave your new fire hole. If it doesn’t collapse in on itself it’s considered a success!
Thanks for reading this post, I hope to be posting some more updates about our foundry in the coming weeks, so watch this space. Also, if you have been making your own foundry, leave a comment below. We would love to hear from you.