Gasless ('MIG') Welding – what causes Porosity and how to fix it

Date: 18-04-2018


Having porosity problems with gasless welding wire?

Porosity (air bubbles or pin holes in the weld metal) not only looks terrible, but it will also significantly weaken the weld joint.

Here’s a checklist to help you diagnose what is causing the problem:


1) Check the Polarity

The wrong polarity will cause porosity and a host of other problems too. Check that your earth lead is connected to positive (+) and the torch/wire to negative (-). If in doubt, check out our article on gasless wire polarity.


2) Pull, don’t push

With Gasless and flux-cored wires, you should always drag the torch (similar to stick electrode welding), so that the torch is pointing back at the weld pool.  A helpful way to remember this is "if there's slag, you drag".
This is the opposite to MIG welding (with gas) where you would normally push the torch. 


3) Adjust Machine Settings & Technique

While the arc may feel smoother with a high voltage, one of the most common causes of porosity is too much voltage (heat).
Try turning down the voltage setting on your welder. (Depending on the material thickness, you may also want to consider changing to a larger diameter wire - this will effectively reduce your voltage whilst allowing a higher weld deposition rate).

Also - the following adjustments can also help to eliminate or reduce porosity;
Increase wire speed
Increase wire stick out length
Decrease travel angle (angle the torch closer to a perpendicular position)

Note that some gasless wires are more sensitive to variations in settings than others and are more prone to porosity problems. One of the reasons why many welders prefer Weldclass Platinum GL-11® gasless wire is because it is very tolerant to variations in machine settings and characteristics, and is very resistant to porosity and other issues.


4) Avoid Very Dirty & Contaminated Metal

Gasless wire is usually more tolerant towards dirt, rust, paint and surface imperfections than standard MIG welding (with gas), however the fact remains that poor surface condition can still cause porosity and other problems.

Also note that sometimes the parent metal can look relatively clean, but has been contaminated with grease or other substances that have penetrated the steel.

If the material being welded is dirty or if you suspect it has been contaminated, prepare a test piece that is completely clean and has not come into contact with oil. If necessary, grind or linish the test piece to ensure contamination is completely removed. Run some test welds on the test piece – if the test welds are free of porosity then it is very likely that surface contamination is the problem. If the test still exhibits porosity, then check the other potential causes in this article.

Some gasless wires are more “fussy” than others about surface condition. Platinum GL-11® wire is very tolerant to imperfect surfaces, making it very easy and hassle-free to use.


5) Check Earth Lead/Clamp & All Connections

It is critical that all components along the ‘current path’ are in good condition and of good quality. Defects at any point can contribute to issues like porosity. This includes:

  • Earth connection to the job/workpiece
  • Earth clamp
  • Earth cable
  • Any point where cable joins to a lug or connector
  • MIG torch and cable
  • Connectors where cables or torches connect to the machine

Check these components and rectify or replace any loose, worn, or poor quality components. Check that the cable connections on the front of the machine are kept tight, these can become loose over time.

If your earth clamp is the 'cheap & nasty' type, we strongly recommend that you upgrade it. The popular Weldclass Platinum Series Heavy-Duty Earth Clamps are very robust, super easy to fit, and suits all welders... and most importantly, designed to provide a very reliable earth connection.

Also note that the earth clamp should be as close to the weld location as possible, to provide the most direct ‘current path’.

Our article & video on earth clamps has some great info on this topic.



6) Avoid Very Windy Conditions

Yes gasless wire is often used in the field and is certainly the best choice for windy conditions. However, if the wind is particularly strong this can cause porosity.

To shield the weld, gasless wire relies on both a slag system and the gases produced from chemical reactions in the arc. Strong wind can interfere with this gas shield, exposing the molten metal to the atmosphere and cause porosity.

If you suspect this might be happening, run some test welds in a sheltered area.


7) Try a better quality wire

Compared to standard solid wire, Gasless wire is much more prone to quality variations from one brand to another.
This is because the performance of the wire is very dependent on the formula of the flux inside the wire, as well as the integrity of the filler metal. While different gasless wire brands may comply with the same classification, each manufacturer will have their own formula and therefore each wire will behave differently.

If the wire you are using is proving difficult to run, try Weldclass Platinum GL-11®. Thousands of Aussie welders rate GL-11® as the best, most user-friendly gasless wire they have ever used... we'd love to get your feedback as well!





This blog is intended to help with:  What causes porosity with gasless wire | How to fix porosity | Air holes and pin holes in a gasless weld.

While all care has been taken, Weldclass accepts no responsibility for any inaccuracies, errors or omissions in this information or links and attachments. Any comments, suggestions & recommendations are of a general nature only and may not apply to particular applications. It is the sole responsibility of the user and/or operator to select the appropriate product for their intended purpose and to ensure that the product selected is capable of performing correctly and safely in the intended application. E.&O.E.

  • Date: 02-04-2020
    Narenders Json Enterprise

    We require gasless mig welding machine
  • Date: 18-06-2018
    John Melotto AJ Enterprises (NSW) Pty Ltd

    I've used alot of different brands of gasless wires of various prizes and rate worldclass as up there with the best been able to multi pass and fill bigger gaps then normal a alround nice gasless wire.