What kind of welding is “flux core” – The ins and outs and everything you need to know

flux-core welding process

Before I started writing this article, I did a little bit of a research to gather my thoughts on what exactly I should write to provide you with as much value as possible. To my surprise, it turns out that much of the information available is tremendously overcomplicated. If you are just starting out, many of you might not understand what flux core welding is, so I did my best to keep things as simple as possible for you.

So without further ado, let’s get right into it.

What it is and how does it work?

If you are a complete novice then it is a welding method like any other. For you to weld, you have to have a machine that takes the electricity from our outlet, transforms it into a suitable current to help us create a heat high enough to melt metals.

Melting two pieces of metal with electricity alone is not enough most of the time though. It would create a bond between metals, but not strong enough to last long or to carry large amounts of weight.

That is why you need to add a filler wire into the mix to fill out the potential caps, which in this case is “Flux-Cored wire”.

Before I explain any further, for you to understand completely, you need to know a few things. The main thing is that when you are melting metal with a welder, the molten material tends to react with air. The reaction with air deforms the weld, thus making it weak. We do not need weak welds, but we need them to last. So you always must have a way to isolate the welding pool (molten metal) from the air. That is when the “flux” comes into play.

Secondly, you need to add the filler metal consistently to the weld to make it uniform. That makes it a wire feel welding method. Because for you to weld, you need to use a machine that is capable of feeding the wire as you go.

The point of my long explanation is, when you start welding, the welder continuously feeds new filler wire into the pool, and since it has flux embedded into it, it will burn because of the high heat. The burning flux cloud will isolate the puddle from the air, making it possible to make strong and nice welding beads.

What is Flux-Cored wire?

As I already mentioned, it is a filler metal that has flux embedded into it. The flux is needed to shield out any gases from the atmosphere. Without isolating the weld, it would have defects and porosity.

There are few different types of wire, some are even used with shielding gases, but as a hobbyist, you probably do not need to know much about that. The more interesting or useful information for you would be the thicknesses of the wire and which one to choose. For that, I have a whole post comparing .030 and .035 wires here.

There are also other ways to shield the puddle form air, one of them would be to use a shielding gas. But we will talk about that later on in this article.

What is Flux Core welding used for and how thick can it weld?

I personally do not like flux-cored welding much because it is messy, and as you can imagine, the shielding gas cloud created is very nasty and toxic, so it is used a lot of times for welding outdoors. There are a couple of reasons for that and the first one would be the fact that regular shielding gas would be carried away by air currents outdoors. The other one, of course, would be because of the toxic gases – it is not really suitable to work with it indoors without adequate ventilation systems. And last but not least, FCAW welders are really portable because they are light in weight and you do not need to carry extra shielding gas bottle with you.

So mainly flux core welding is used for construction and outdoor repairs. Repairs and construction because is actually a really forgiving welding method, and due to the self-shielding properties, it is more suitable to use on dirtier surfaces. The thicknesses you can tackle are pretty good as well. Without huge amperages (up to 140), according to some manufacturers, you can weld up to a quarter of an inch. Quarter, in my opinion, is a bit too much and I would not advise you to start out welding materials that thick, but it can weld very thick materials depending on the machine you are using.

Is MIG and flux-core the same and which is better?

MIG and flux are pretty similar. They both use filler wire that is continuously fed to your welds, but still, they are not the same.

So for MIG welding, instead of a flux embedded wire, a regular filler is used. To shield the welding pool, shielding gas is used. Most of the time it would be pure CO2 or a mix with argon.

Since the flux is missing in this case, the welds are cleaner, a lot less messy and due to that they do not need as much post-weld cleanup. It also produces less toxic gases. For me, MIG always wins, but in some cases, flux is still better.

As we already discussed, regular shielding can not be used outdoors because of the wind and airflow. That is when the flux core would be the way to go.

Flux machines are also cheaper, so if you are just starting out, going only flux would be a thing to consider to get your feet wet in welding. If you are looking for a cheap FCAW welder, click the previous link, where I recommend one.

Can I use self-shielded wire in a MIG machine?

In most cases, if not all, yes you can use MIG machine for FCAW. For that, there are a couple of steps you need to make. First of all, you need to change the polarity of the machine. It is usually done from the inside of the machine. You just need to unscrew two bolts and switch the wires. It should be, when you used the machine for MIG, DCEP. And change it to DCEN. DC means direct current and respectively EP Electrode Positive to EP – Electrode Negative. And yes, in this case, electrode stands for filler wire.

Nevertheless, I would recommend you to check it out from your user manual.

The one thing that some of you might think – if that is so easy, can I use my FCAW machine for MIG as well? Usually, the answer to that is no. If you bought a regular flux machine then more than likely you do not have the option to use a shielding gas.

Is it the best method for beginners?

In terms of budget, it is the most pocket-friendly way to start off your venture as a new hobby welder or an artist. However, it has its own limitations and downsides. A few of these would be that the cheap flux core welders handle a bit more differently and are not as easy to weld with as a beginner.

Yes you can throw mud at the wall and something will stick, but at the end of the day, it is much more difficult to get good results with flux core as a beginner. It is way easier to use regular MIG with CO2. That way you will probably shorten your learning curve a lot.

Another thing with flux machines is that you really can not weld very thin materials because of the post-weld cleanup and due to the nature of the welding arc itself, it tends to burn through the material and the cleanup on thin material is much more difficult to do. With thin metal, you just can not use a huge chipping hammer to pound off the slag without damaging the base metal that the flux left behind.

The things you need to remember when starting out

There is nothing wrong or bad to start with FCAW, but if you are a beginner, you also need to make a small investment to buy safety equipment and some tools. First of all, you need a welding helmet and gloves for welding. They are the bare minimum you need. I would also buy a Fire-resistant welding jacket to avoid burning my arms with sparks.

From the tool’s side, assuming you have something to cut metals and measure them, you need at least a chipping hammer and a wire brush to remove the slag.


To sum it all up, flux-core welding is a simple welding method that uses a filler wire that is fed into the weld puddle. It is really forgiving and simple way to bond metals and also a budget-friendly way to start off as a new welder or fix a thing or two around the house yourself. It has its own pros and cons, but at the end of the day, it does not matter how you achieve what you want, what matters is that you take action.